Remove support using older android build tools when signing 14.5 releases in tools/signing/wrappers/sign-apk

We have those lines that can be removed from tools/signing/wrappers/sign-apk:

  # If signing 14.5, keep using android-12 build tools
  # (we can remove this when 15.0 is the stable release)
  ( test -z "$tbb_version" || echo "$tbb_version" | grep -q '^14\.5' ) && \
    abt_version=12