Remove defunct DESCRIP.MMS cleanup rules.

Remove defunct DESCRIP.MMS cleanup rules.

Rules to remove C and object files from vms/ext were made redundant when
commit 26dd53a231877708 in Sep 2009 moved the XS extensions from there to
ext/

The wildcard rule to remove t/lib/vms*.t, which has been in
vms/descrip_mms.template since the file was added by commit 97abc6adffcd3efc
in June 1998 was effectively made redundant when it was duplicated by 4
specific rules for the 4 files it matched added by commit 493ba88a837f5a6b
in June 2001.

The rule to delete t/lib/vmsish.t was made redundant when vms/ext/vmsish.*
were moved to lib/ by commit 9f84c00564fd021b in Nov 2001.