Remove SSL_CTRL_SET_CLIENT_CERT_TYPES.

This isn't called and, with the fixed-DH client cert types removed, is
only useful if a server wishes to not accept ECDSA certificates or
something.

BUG=404754

Change-Id: I21d8e1a71aedf446ce974fbeadc62f311ae086db
Reviewed-on: https://boringssl-review.googlesource.com/5673
Reviewed-by: Adam Langley <agl@google.com>