xfree86: finish removing numTimings in xf86ValidateModes()

Finishes the work started in commit cd0d4c1b
to remove checks for the variable that never varied from 0 after the code
to change it was removed by commit 511c60bc
in 2006 (xorg-server-1.2.0).

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