sequoia-openpgp: fully strip unwanted optional deps

just removing them from the features table is not enough, as cargo interprets optional deps without any feature "reverse-dependency" as "must provide automatic feature", which is the opposite of what the 'dep:' prefix is supposed to achieve.

confirmed the resulting d/control Provides list matches cargo metadata's view of the features provided by sequoia-openpgp. none of these optional deps are provided as features without the cleanup-deps patch in the first place, so nothing should depend on them either.

Signed-off-by: Fabian Grünbichler debian@fabian.gruenbichler.email