Remove deprecated functions and types

src/decryptionresult.h (unsupportedAlgortihm, wrongKeyUsage): Remove.
src/key.h (Key::canReallySign, Key::isSecret,
UserID::Signature::Notation, non-const UserID::Signature::operator<
overload): Remove.
src/keygenerationresult.h (KeyGenerationResult::primaryKeyGenerated,
KeyGenerationResult::subkeyGenerated): Remove.
src/verificationresult.h (Signature::Notation,

Signature::wrongKeyUsage): Remove.

Remove functions and types that are deprecated since quite some time.