Newer versions of FIPS don't need any special casing in our bindings,
unlike the submoduled boringssl-fips. In addition, many users currently
use FIPS by precompiling BoringSSL with the proper build tools and
passing that in to the bindings.

Until we adopt the Update Stream pattern for FIPS, there are two main
use cases:

1. Passing an unmodified, precompiled FIPS validated version of
   boringssl (fips-precompiled)

2. Passing a custom source directory of boringssl meant to be linked
   with a FIPS validated bcm.o. This is mainly useful if you carry
   custom patches but still want to use a FIPS validated BoringCrypto.
   (fips-link-precompiled)

This commit introduces the `fips-precompiled` feature and removes the
`fips-no-compat` feature.