COMP: Clear VTK_HAS_STD_ISFINITE and related variables.

The cmake variables VTK_HAS_STD_ISFINITE, VTK_HAS_STD_ISNAN, and
VTK_HAS_STD_ISINF were set incorrectly prior to commit c4b4eb3b,
and the incorrect settings are stuck in the CMakeCache.txt of many
machines (and will be until they clear their cache).  So this commit
specifically removes those variables from the cache, in order to
allow the correct checks to be done.  This commit will be reverted
after one week.

Change-Id: I27073fbe199957a551c65c090313d74a850b28db
Merge topic 'clear-std-isfinite' into master

f1760ede COMP: Clear VTK_HAS_STD_ISFINITE and related variables.