Update COMP_METHOD

Update COMP_METHOD

size_t-ify the COMP_METHOD structure and functions.
Get rid of the non-functional COMP_METHODS and return NULL instead.

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Hugo Landau <hlandau@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/18186)