Revert Sequoia signing support for now, breaks CI
    
    Running a build through the RHEL OSCI reveals some possible shortcomings
    of the original design:
    
    - Custom macros using %__gpg may now easily break if the Sequoia backend
      is installed, such as those overriding %__gpg_sign_cmd where %__gpg is
      typically the first argument, followed by CLI options only known to
      GnuPG.  This is exactly the case with some of our Beaker tests.
    
    - Some tests attempt to install both subpackages directly with dnf which
      obviously fails as they conflict with each other.  This is just a test
      issue, though.
    
    Therefore, the boolean dependency in rpm-sign-libs declaring that both
    implementations are equally compatible is just wrong, until we can prove
    otherwise, by making the CI tests pass, for starters.
    
    Drop the Sequoia subpackage for now.  This is less drastic than a full
    revert since the actual GnuPG split-off is still reasonable on its own.
    We can always add Sequoia support back later, once we figure out the
    above issues.
    
    Related: RHEL-56363