Remove dead code for use v5

Dies while complaining about missing `Perl5` module. A thought occured
to make it load Inline::Perl5, but felt like useless magic, so I
removed the code entirely and just make it complain there's no
compiler for v5, like it'd do for `use v6.z`

Fixes RT#130834: https://rt.perl.org/Ticket/Display.html?id=130834

src/Perl6/Grammar.nqp

@@ -1607,11 +1607,6 @@ grammar Perl6::Grammar is HLL::Grammar does STD {
                     # we parse out the numeral, since we could have "6c"
                     :my $version := nqp::radix(10,$<version><vnum>[0],0,0)[0];
                     [
-                    ||  <?{ $version == 5 }> {
-                            my $module := $*W.load_module($/, 'Perl5', {}, $*GLOBALish);
-                            $*W.do_import($/, $module, 'Perl5');
-                            $*W.import_EXPORTHOW($/, $module);
-                        }
                     ||  <?{ $version == 6 }> {
                             my $version_parts := $<version><vnum>;
                             my $vwant := $<version>.ast.compile_time_value;

t/05-messages/01-errors.t

@@ -225,6 +225,9 @@ subtest '`IO::Socket::INET.new: :listen` fails with useful error' => {
     like $res.exception.message, /'Invalid port'/, 'error mentions port';
 }
 
+throws-like ｢use v5｣, X::Language::Unsupported,
+    '`use v5` in code does not try to load non-existent modules';
+
 done-testing;
 
 # vim: ft=perl6 expandtab sw=4