Clean up references to FIPS

This removes the fips configure option. This option is broken as the
required FIPS code is not available.

FIPS_mode() and FIPS_mode_set() are retained for compatibility, but
FIPS_mode() always returns 0, and FIPS_mode_set() can only be used to
turn FIPS mode off.

Reviewed-by: Stephen Henson <steve@openssl.org>