Generate postgis_svn_revision.h

If Git revision is available, set SVN revision to fake number 1.
TODO: Fetch SVN revision
Generate postgis_svn_revision.h using utils/svn_repo_revision.pl script.

Remove previously added CMake modules for Git revision retrival.
Generate postgis_svn_revision.h using utils/svn_repo_revision.pl script.

Remove previously added CMake modules for Git revision retrival.