Remove unused old perl test script `check-rdiff`.
Remove unused old perl test script `check-rdiff`.

This looks like it was once one of the main rdiff test scripts, but it is
nolonger used and other tests provide better coverage.

dbaarda/librsync,dbaarda/librsync,librsync/librsync,sourcefrog/librsync,librsync/librsync,dbaarda/librsync,librsync/librsync,sourcefrog/librsync,librsync/librsync,sourcefrog/librsync,sourcefrog/librsync,dbaarda/librsync