Clean up issuance-time OCSP code

[aarongable]

We've configured all of our production profiles to exclude the AIA OCSP URI from our certificates. We can now remove the code which supported:

• including AIA OCSP URIs in certs
• including the MustStaple extension in certs
• configuring profiles to include or not include them
• conditioning MustStaple inclusion on an allow-list

We should continue rejecting any finalize requests which include the MustStaple extension in their CSR.

The two sub-issues track the removal of the critical code and the deprecation of the corresponding config items; this issue will track the final removal of those config items after they have been removed from all deployed configs.