Remove no-longer-used name variable in _XGetAtomName

Fixes gcc warning:
GetAtomNm.c: In function ‘_XGetAtomName’:
GetAtomNm.c:39:11: warning: unused variable ‘name’ [-Wunused-variable]
     char *name;
           ^~~~

Introduced by commit 336c1e7a

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>