Wrap more of ocspapitest.c in OPENSSL_NO_OCSP

make_dummy_resp() uses OCSP types, and get_cert_and_key() is unused
once make_dummy_resp() is compiled out, so neither can be included
in the build when OCSP is disabled and strict warnings are active.

Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4873)