Suppress occasional failures in brin regression test.

brin.sql included a call of brin_summarize_new_values(), and expected
it to always report exactly 5 summarization events.  This failed sometimes
during parallel regression tests, as a consequence of the database-wide
VACUUM in gist.sql getting there first.  The most future-proof way
to avoid variation in the test results is to forget about using
brin_summarize_new_values() and just do a plain "VACUUM brintest",
which will exercise the same code anyway.

Having done that, there's no need for preventing autovacuum on brintest;
doing so just reduces the scope of test coverage, so let's not.

src/test/regress/expected/brin.out

@@ -26,7 +26,7 @@ CREATE TABLE brintest (byteacol bytea,
 	int4rangecol int4range,
 	lsncol pg_lsn,
 	boxcol box
-) WITH (fillfactor=10, autovacuum_enabled=off);
+) WITH (fillfactor=10);
 INSERT INTO brintest SELECT
 	repeat(stringu1, 8)::bytea,
 	substr(stringu1, 1, 1)::"char",
@@ -239,11 +239,6 @@ INSERT INTO brintest SELECT
 	format('%s/%s%s', odd, even, tenthous)::pg_lsn,
 	box(point(odd, even), point(thousand, twothousand))
 FROM tenk1 LIMIT 5 OFFSET 5;
-SELECT brin_summarize_new_values('brinidx'::regclass);
- brin_summarize_new_values 
----------------------------
-                         5
-(1 row)
-
+VACUUM brintest;  -- force a summarization cycle in brinidx
 UPDATE brintest SET int8col = int8col * int4col;
 UPDATE brintest SET textcol = '' WHERE textcol IS NOT NULL;

src/test/regress/sql/brin.sql

@@ -26,7 +26,7 @@ CREATE TABLE brintest (byteacol bytea,
 	int4rangecol int4range,
 	lsncol pg_lsn,
 	boxcol box
-) WITH (fillfactor=10, autovacuum_enabled=off);
+) WITH (fillfactor=10);
 
 INSERT INTO brintest SELECT
 	repeat(stringu1, 8)::bytea,
@@ -247,7 +247,7 @@ INSERT INTO brintest SELECT
 	box(point(odd, even), point(thousand, twothousand))
 FROM tenk1 LIMIT 5 OFFSET 5;
 
-SELECT brin_summarize_new_values('brinidx'::regclass);
+VACUUM brintest;  -- force a summarization cycle in brinidx
 
 UPDATE brintest SET int8col = int8col * int4col;
 UPDATE brintest SET textcol = '' WHERE textcol IS NOT NULL;