This change removes two mechanisms that are deprecated in RFC 4880. The
spec explicitly mentions that "RSA Encrypt-Only (2) and RSA Sign-Only
are deprecated and SHOULD NOT be generated" [0].
The remaining RSA_GENERAL key type was renamed to just RSA for ease of
use for developers.
[0]: https://tools.ietf.org/html/rfc4880#section-9.1