Back out some changes to docs Makefiles

Commit ab0e9dbfa7 introduced some changes
to the documentation Makefiles designed to clean-up the process of
deciding which headers get scanned for the docs.

Unfortunately, the gtk-doc Makefile doesn't use HFILE_GLOB for actually
generating the docs -- only for knowing when it needs to redo the
generation.  Because of this, we need to use IGNORE_HFILES or otherwise
we get hundreds of symbols in the *-unused.txt files.

Revert the changes that that commit made to the docs Makefiles (but
leave the generation of the *-public-headers.txt files in place).

docs/reference/gobject/Makefile.am

@@ -20,9 +20,16 @@ SCAN_OPTIONS=--deprecated-guards="G_DISABLE_DEPRECATED" \
 MKDB_OPTIONS=--sgml-mode --output-format=xml --name-space=g
 
 # Used for dependencies
-HFILE_GLOB=$(addprefix $(top_srcdir)/gobject/,$(shell cat $(top_builddir)/gobject/gobject-public-headers.txt))
+HFILE_GLOB=$(top_srcdir)/gobject/*.h
 CFILE_GLOB=$(top_srcdir)/gobject/*.c
 
+# Headers to ignore
+IGNORE_HFILES = \
+	tests			\
+	gobject_trace.h		\
+	gatomicarray.h
+
+
 # CFLAGS and LDFLAGS for compiling scan program. Only needed
 # if $(DOC_MODULE).types is non-empty.
 INCLUDES = \