Set patchable: false for OCSP tasks

[eramongodb]

Disables inclusion of OCSP tasks in patch builds.

Motivated by the OCSP Support Test Plan instructions which states:

[...] each Evergreen task SHOULD set a batchtime of 14 days to reduce how often these tests run (this will not affect patch builds).

The OCSP tasks can be re-enabled for patch builds as needed by temporarily setting task['patchable'] = True when submitting patch builds.

As a drive-by improvement, also removes redundant specification of the ubuntu2004-small distro for tasks in the ocsp variant.