gpg: Simplify the compliance settings.

* g10/gpg.c (set_compliance_option): Base most settings on oGnuPG.
For oGnuPG explictly clear the allow_old_cipher_algos flag.

Note that --allow-old-cipher-algos must now come after a compliance
settings. This avoids a bug when first setting oRFC2440 and then
oGnuPG which would not clear the flag.

• GnuPG-bug-id: T7501