Remove an unstable wait from parallel autovacuum regression test.

The test 001_parallel_autovacuum.pl verified that vacuum delay
parameters are propagated to parallel vacuum workers by using
injection points. It previously waited for autovacuum to complete on
the test_autovac table. However, since injection points are
cluster-wide, an autovacuum worker could be triggered on tables in
other databases (e.g., template1) and get stuck at the same injection
point. This could lead to a timeout when the test waits for the
expected table's autovacuum to finish.

This commit removes the wait for autovacuum completion from this
specific test case. Since the primary goal is to verify the
propagation of parameter updates, which is already confirmed via log
messages, waiting for the entire vacuum process to finish is
unnecessary and prone to instability in concurrent test environments.

Author:	Sami Imseih <samimseih@gmail.com>
Discussion: https://postgr.es/m/CAA5RZ0s+kZZRMSF4HW7tZ9W2jS1o4B+Fg8dr5a-T6mANX+mdQA@mail.gmail.com

src/test/modules/test_autovacuum/t/001_parallel_autovacuum.pl

@@ -177,8 +177,6 @@ $node->wait_for_log(
 	qr/parallel autovacuum worker updated cost params: cost_limit=500, cost_delay=5, cost_page_miss=10, cost_page_dirty=10, cost_page_hit=10/,
 	$log_offset);
 
-wait_for_autovacuum_complete($node, $av_count);
-
 # Cleanup
 $node->safe_psql(
 	'postgres', qq{