Remove custom "Build-Id" field from manifest. It contains:
* Timestamp: Makes the build unreproducible.
* Architecture: Makes the build arch-dependent whereas we want it as
  noarch.:
* OS and Java version: Too detailed information, triggers too many
  publication for no real advantage.

--
diff -up fop-2.1/build.xml.orig fop-2.1/build.xml
--- fop-2.1/build.xml.orig	2018-10-29 07:26:58.205413821 +0100
+++ fop-2.1/build.xml	2018-10-29 07:55:33.117484917 +0100
@@ -460,7 +460,6 @@ list of possible build targets.
         <attribute name="Implementation-Title" value="${Name}"/>
         <attribute name="Implementation-Version" value="${version}"/>
         <attribute name="Implementation-Vendor" value="The Apache Software Foundation (http://xmlgraphics.apache.org/fop/)"/>
-        <attribute name="Build-Id" value="${ts} (${user.name} [${os.name} ${os.version} ${os.arch}, Java ${java.runtime.version}, Target Java ${javac.target}])"/>
       </manifest>
     </jar>
   </target>
@@ -482,7 +481,6 @@ list of possible build targets.
     <jar jarfile="${build.dir}/fop.jar" basedir="${build.classes.dir}">
       <manifest>
         <attribute name="Main-Class" value="org.apache.fop.cli.Main"/>
-        <attribute name="Build-Id" value="${ts} (${user.name} [${os.name} ${os.version} ${os.arch}, Java ${java.runtime.version}, Target Java ${javac.target}])"/>
         <section name="org/apache/fop/">
           <attribute name="Specification-Title" value="XSL-FO - Extensible Stylesheet Language"/>
           <attribute name="Specification-Version" value="1.1"/>
@@ -506,9 +504,7 @@ list of possible build targets.
       <format property="ts" pattern="yyyyMMdd-HHmmss-z"/>
     </tstamp>
     <jar jarfile="${build.dir}/fop-sandbox.jar" basedir="${build.sandbox-classes.dir}">
-      <manifest>
-        <attribute name="Build-Id" value="${ts} (${user.name} [${os.name} ${os.version} ${os.arch}, Java ${java.runtime.version}, Target Java ${javac.target}])"/>
-      </manifest>
+      <manifest/>
       <metainf dir="${basedir}" includes="LICENSE,NOTICE"/>
     </jar>
   </target>
@@ -637,7 +633,6 @@ list of possible build targets.
         <attribute name="Implementation-Title" value="${fop-transcoder.name}"/>
         <attribute name="Implementation-Version" value="${fop-transcoder.version}"/>
         <attribute name="Implementation-Vendor" value="The Apache Software Foundation (http://xmlgraphics.apache.org/fop/)"/>
-        <attribute name="Build-Id" value="${ts} (${user.name} [${os.name} ${os.version} ${os.arch}, Java ${java.runtime.version}, Target Java ${javac.target}])"/>
       </manifest>
       <metainf dir="${basedir}" includes="LICENSE,NOTICE"/>
     </jar>
@@ -672,7 +667,6 @@ list of possible build targets.
         <attribute name="Implementation-Title" value="${fop-transcoder.name}"/>
         <attribute name="Implementation-Version" value="${fop-transcoder.version}"/>
         <attribute name="Implementation-Vendor" value="The Apache Software Foundation (http://xmlgraphics.apache.org/fop/)"/>
-        <attribute name="Build-Id" value="${ts} (${user.name} [${os.name} ${os.version} ${os.arch}, Java ${java.runtime.version}, Target Java ${javac.target}])"/>
       </manifest>
       <metainf dir="${basedir}" includes="LICENSE,NOTICE"/>
     </jar>
@@ -1042,9 +1036,7 @@ NOTE:
   </target>
   <target name="jar-javadocs" depends="javadocs" description="Generates a jar file containing the Javadocs">
     <jar jarfile="${build.dir}/${name}-${version}-javadoc.jar">
-      <manifest>
-        <attribute name="Build-Id" value="${ts} (${user.name} [${os.name} ${os.version} ${os.arch}, Java ${java.runtime.version}, Target Java ${javac.target}])"/>
-      </manifest>
+      <manifest/>
       <fileset dir="${build.javadocs.dir}"/>
       <metainf dir="${basedir}" includes="LICENSE,NOTICE"/>
     </jar>
@@ -1346,9 +1338,7 @@ NOTE:
       <param name="pwd" value="${pwd}"/>
     </antcall>
     <jar jarfile="${build.dir}/${name}-${version}-bundle.jar">
-      <manifest>
-        <attribute name="Build-Id" value="${ts} (${user.name} [${os.name} ${os.version} ${os.arch}, Java ${java.runtime.version}])"/>
-      </manifest>
+      <manifest/>
       <fileset dir="${build.dir}">
         <patternset>
           <include name="${name}-${version}.jar*"/>
diff -up fop-2.1/examples/plan/build.xml.orig fop-2.1/examples/plan/build.xml
--- fop-2.1/examples/plan/build.xml.orig	2018-10-29 07:48:15.749466784 +0100
+++ fop-2.1/examples/plan/build.xml	2018-10-29 07:48:22.709467073 +0100
@@ -133,7 +133,6 @@
         <attribute name="Implementation-Title" value="${Name}"/>
         <attribute name="Implementation-Version" value="${version}"/>
         <attribute name="Implementation-Vendor" value="Apache Software Foundation (http://xmlgraphics.apache.org/fop/)"/>
-        <attribute name="Build-Id" value="${ts} (${user.name} [${os.name} ${os.version} ${os.arch}])"/>
     </manifest>
     </jar>
   </target>