Shorten the title for D-Bus interface docs

The title of an interface can be arbitrarily long, considering that
reverse DNS namespaces can be pretty complex. Instead of using the whole
interface name, we can use the name without the prefix.

gio/gdbus-2.0/codegen/codegen_md.py

@@ -88,7 +88,7 @@ class MdCodeGenerator:
             f"Title: {iface.name} D-Bus Interface",
             f"Slug: {iface.name}",
             "",
-            "# " + iface.name,
+            "# " + iface.name_without_prefix,
             "",
             "## Description",
             "",

gio/gdbus-2.0/codegen/codegen_rst.py

@@ -82,12 +82,13 @@ class RstCodeGenerator:
 
     def _generate_header(self, iface):
         """Generates the header and preamble of the document."""
-        header_len = len(iface.name)
+        iface_name = iface.name_without_prefix
+        header_len = len(iface_name)
         res = [
             f".. _{iface.name}:",
             "",
             "=" * header_len,
-            iface.name,
+            iface_name,
             "=" * header_len,
             "",
             "-----------",