pgsql: Reduce the last group of parallel regression tests to 19 tests,

[tgl(at)postgresql(dot)org (Tom Lane)]

Log Message:
-----------
Reduce the last group of parallel regression tests to 19 tests, per failure
on buildfarm member bear.  Sync the test order in serial_schedule with that
in parallel_schedule.

Modified Files:
--------------
    pgsql/src/test/regress:
        parallel_schedule (r1.52 -> r1.53)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/parallel_schedule?r1=1.52&r2=1.53)
        serial_schedule (r1.49 -> r1.50)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/src/test/regress/serial_schedule?r1=1.49&r2=1.50)