Fix vcregress.pl for new plperl test case.
As of commit the plperl tests don't want preinstalled
plperl languages; they now install those themselves.  I'd removed the
load-extension options from the GNUmakefile, but missed teaching
the MSVC build script about that.
Per buildfarm.
@@ -353,8 +353,8 @@ sub plcheck
if ($lang eq 'plperl')
{
- # run both trusted and untrusted perl tests
- push(@lang_args, "--load-extension=plperlu");
+ # plperl tests will install the extensions themselves
+ @lang_args = ();
# assume we're using this perl to built postgres
# test if we can run two interpreters in one backend, and if so
