Replace Test::More plans with done_testing

Rather than doing manual book keeping to plan the number of tests to run
in each TAP suite, conclude each run with done_testing() summing up the
the number of tests that ran. This removes the need for maintaning and
updating the plan count at the expense of an accurate count of remaining
during the test suite runtime.

This patch has been discussed a number of times, often in the context of
other patches which updates tests, so a larger number of discussions can
be found in the archives.

Reviewed-by: Julien Rouhaud <rjuju123@gmail.com>
Reviewed-by: Dagfinn Ilmari Mannsåker <ilmari@ilmari.org>
Reviewed-by: Tom Lane <tgl@sss.pgh.pa.us>
Reviewed-by: Michael Paquier <michael@paquier.xyz>
Reviewed-by: Kyotaro Horiguchi <horikyota.ntt@gmail.com>
Discussion: https://postgr.es/m/DD399313-3D56-4666-8079-88949DAC870F@yesql.se

src/test/perl/README

@@ -54,8 +54,7 @@ Each test script should begin with:
     use warnings;
     use PostgreSQL::Test::Cluster;
     use PostgreSQL::Test::Utils;
-    # Replace with the number of tests to execute:
-    use Test::More tests => 1;
+    use Test::More;
 
 then it will generally need to set up one or more nodes, run commands
 against them and evaluate the results. For example:
@@ -69,6 +68,10 @@ against them and evaluate the results. For example:
 
     $node->stop('fast');
 
+Each test script should end with:
+
+	done_testing();
+
 Test::More::like entails use of the qr// operator.  Avoid Perl 5.8.8 bug
 #39185 by not using the "$" regular expression metacharacter in qr// when also
 using the "/m" modifier.  Instead of "$", use "\n" or "(?=\n|\z)".