crypto: bypass FIPS_mode if not compiled for FIPS

[rvagg]

This isn't strictly necessary but it's the remaining piece of FIPS code that is exposed in a build that hasn't been compiled with FIPS enabled. So, it's for consistency sake, mainly.

/R=@nodejs/crypto

[rvagg]

CI @ https://ci.nodejs.org/job/node-test-commit/5867/

[bnoordhuis]

FIPS_mode() is always available, whether FIPS is enabled or not, so this could be simplified to just args.GetReturnValue().Set(FIPS_mode()) - no compile- or run-time branches.

[indutny]

There is no need in guarding FIPS_mode(), it works correctly. I don't mind adding a test, though.

[rvagg]

I had an ulterior motive here regarding alt-ssl libraries but that's not an immediate concern so I'll close this for now and revisit later since it doesn't pass the sniff test as a standalone change.