Remove useless and rather expensive stanza in matview regression test.

Remove useless and rather expensive stanza in matview regression test.

This removes a test case added by commit b69ec7cc9, which was intended
to exercise a corner case involving the rule used at that time that
materialized views were unpopulated iff they had physical size zero.
We got rid of that rule very shortly later, in commit 1d6c72a55, but
kept the test case.  However, because the case now asks what VACUUM
will do to a zero-sized physical file, it would be pretty surprising
if the answer were ever anything but "nothing" ... and if things were
indeed that broken, surely we'd find it out from other tests.  Since
the test involves a table that's fairly large by regression-test
standards (100K rows), it's quite slow to run.  Dropping it should
save some buildfarm cycles, so let's do that.

Discussion: https://postgr.es/m/32386.1493831320@sss.pgh.pa.us