json: Remove subkey-algo from createkey command.

* src/gpgme-json.c (op_createkey): Remove subkey-algo param.
(GPG_AGENT_ALLOWS_KEYGEN_TRHOUGH_BROWSER): Fix typo.
* lang/js/src/Keyring.js: Remove subkey-algo support.
* lang/js/src/permittedOperations.js: Ditto.

We do not want to expose details of the protocol's key generation and
thus the subkey-algo does not make sense. Right now we support only
the default and future-default algorithms. A user can configure them
anyway using new-default-key-algo in gpg.conf. Eventually we may
officially support a more flexible way of creating special structured
OpenPGP keys but right now that is not part of the API.

• Signed-off-by: Werner Koch <wk@gnupg.org>