gpg: Remove the extra prompt for Curve25519.
* g10/keygen.c (MY_USE_ECDSADH): New macro local to ask_curve. (ask_curve): Use a fixed table of curve names and reserve a slot for Curve448. Simplify CurveNNNN/EdNNNN switching. (ask_curve): Remove the Curve25519 is non-standard prompt.
Given that ECC generation is only available in export mode and that
gpg will in any case support our current ed2559/cv25519 definition the
extra prompt does not make anymore sense.
- Signed-off-by: Werner Koch <wk@gnupg.org>