Clean up after TAP tests in oid2name and vacuumlo.

Clean up after TAP tests in oid2name and vacuumlo.

Oversights in commits 1aaf532de and bfea331a5.  Unlike the case for
traditional-style REGRESS tests, pgxs.mk doesn't have any builtin support
for TAP tests, so it doesn't realize it should remove tmp_check/.
Maybe we should build some actual pgxs infrastructure for TAP tests ...
but for the moment, just remove explicitly.