Clean up get_tls_handhake_key()

Clean up get_tls_handhake_key()

This function has *much* more code than required.  This commit cleans up
the function:
 * Merge the handling of inline and non-inline code.
 * Don't double-check key.2, since must_have_n_keys() already does that
   (but keep the message about dropped passphrase support in 2.4).
 * Remove stale references to 'passphrase' - we no longer support those

This commit should not change any behaviour except for log messages.

v2: Leave message about dropped passphrase support in place - this option
    was dropped in 2.4, so it is indeed better to be clear about it.

Signed-off-by: Steffan Karger <steffan@karger.me>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <1456151046-16047-1-git-send-email-steffan@karger.me>
URL: http://article.gmane.org/gmane.network.openvpn.devel/11238
Signed-off-by: Gert Doering <gert@greenie.muc.de>