Remove obsolete gconf setup assistant.

Gconf is being replaced by gsettings. The problem the obsolete assistant
is trying to solve will be solved differently for gsettings: in order
to locate the gsettings schema files, the XDG_DATA_DIR environment
variable will be set.

This is already configured for development builds. It's likely this
still has to be set up properly for the Windows/OS X installers

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/trunk@23223 57a11ea4-9604-0410-9ed3-97b8803252fd