Do not set CHPL_REGEXP and CHPL_GMP in nightly testing.

The new speculative build will enable these when possible.
Remove CHPL_REGEXP and CHPL_GMP settings for knc.

Let the speculative build figure it out instead.
Merge pull request #438 from thomasvandoren/use-default-for-gmp-re2

Do not set CHPL_REGEXP and CHPL_GMP in nightly testing.

The new speculative build will enable these when possible.

reviewed by @bradcray