Remove isolation test reindex-partitions

The isolation test added by a6642b3 is proving to be unstable, as once
the first transaction holding a lock on the top-most partitioned table
or on a partition commits, the commit order of the follow-up DROP TABLE
and REINDEX could become reversed depending on the timing.

The only part of the test that could be entirely reliable is the one
using a SHARE lock, allowing REINDEX to commit first, but it is the
least interesting of the set.

Per buildfarm members rorqual and mylodon.

Discussion: https://postgr.es/m/[email protected]

Author: michaelpq

src/test/isolation/expected/reindex-partitions.out

@@ -50,7 +50,6 @@ test: lock-committed-keyupdate
 test: update-locked-tuple
 test: reindex-concurrently
 test: reindex-schema
-test: reindex-partitions
 test: propagate-lock-delete
 test: tuplelock-conflict
 test: tuplelock-update