build_core: don't echo diagnostic revision line. It's no longer needed for diagnosis since a long time, and now since the revisionstring is a command to set the SOURCEREVISION and SUBMODULEREVISIONS with 'eval' and { within it it looks scarier than it is.

git-svn-id: https://rebeccablackos.svn.sourceforge.net/svnroot/rebeccablackos@2940 56e3d1a8-0179-4092-b3e2-9fbbcda0c0a9