[ssl] Prefer SSL_k(EC)?DHE to the SSL_kE(EC)?DH alias

[ssl] Prefer SSL_k(EC)?DHE to the SSL_kE(EC)?DH alias

`SSL_kECDHE` and `SSL_kEECDH`, and `SSL_kDHE` and `SSL_kEDH` are already
marked as aliases of each other in the headers.
This commit, for each pair, replaces the leftover uses of the latter
synonym with the first one, which is considered more common.

Reviewed-by: Dmitry Belyavskiy <beldmit@gmail.com>
Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17763)