cp: remove redundant possibly expensive heap deallocation

If the hash structures grow sufficiently large so that
the system is actively swapping, then the deallocation
can take a significant amount of time.  Details at:
http://lists.gnu.org/archive/html/coreutils/2014-08/msg00012.html

* src/cp.c (main): Only call hash deallocation routines
when in lint checking mode.
* THANKS.in: Remove as now in the git author list.