Back out the session_start and session_end hooks feature.

It's become apparent during testing that there are problems with at
least the testing regime. I don't think we should have it without a
working test regime, and the difficulties might indicate implementation
problems anyway, so I'm backing out the whole thing until that's sorted
out.

This reverts commits 7459484 9989f92 cd8ce3a

src/tools/msvc/vcregress.pl

@@ -383,8 +383,6 @@ sub modulescheck
 	my $mstat = 0;
 	foreach my $module (glob("*"))
 	{
-		# test_session_hooks can't run installcheck, so skip it here
-		next if $module eq 'test_session_hooks';
 		subdircheck("$topdir/src/test/modules", $module);
 		my $status = $? >> 8;
 		$mstat ||= $status;