Make de-vs compliance checks more rigid

Deprecate Formatting::complianceMode() and make all using code use one
of the new helpers for checking de-vs compliance of GnuPG.

The general rule is: If GnuPG doesn't pass the basic de-vs compliance
check, then it makes no sense to label anything as de-vs compliant.

• GnuPG-bug-id: T5362