Drop libimplementations.a

Drop libimplementations.a

libimplementations.a was a nice idea, but had a few flaws:

1.  The idea to have common code in libimplementations.a and FIPS
    sensitive helper functions in libfips.a / libnonfips.a didn't
    catch on, and we saw full implementation ending up in them instead
    and not appearing in libimplementations.a at all.

2.  Because more or less ALL algorithm implementations were included
    in libimplementations.a (the idea being that the appropriate
    objects from it would be selected automatically by the linker when
    building the shared libraries), it's very hard to find only the
    implementation source that should go into the FIPS module, with
    the result that the FIPS checksum mechanism include source files
    that it shouldn't

To mitigate, we drop libimplementations.a, but retain the idea of
collecting implementations in static libraries.  With that, we not
have:

libfips.a

    Includes all implementations that should become part of the FIPS
    provider.

liblegacy.a

    Includes all implementations that should become part of the legacy
    provider.

libdefault.a

    Includes all implementations that should become part of the
    default and base providers.

With this, libnonfips.a becomes irrelevant and is dropped.
libcommon.a is retained to include common provider code that can be
used uniformly by all providers.

Fixes #15157

Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/15171)