Tests: h2_limit_req.t cleanup.

Amended efc502e696b0 that removes checks used prior to body preread buffer.
While here, set a resonable commentary.

Author: pluknet

h2_limit_req.t

@@ -101,9 +101,8 @@ $frames = $s->read(all => [{ sid => $sid, fin => 1 }]);
 ($frame) = grep { $_->{type} eq "HEADERS" } @$frames;
 is($frame->{headers}->{':status'}, 200, 'request body - limit req - empty');
 
-# predict send windows
+# request body sent along with request
 
-$sid = $s->new_stream();
 $s = Test::Nginx::HTTP2->new();
 $sid = $s->new_stream({ path => '/proxy_limit_req/', body => 'TEST2' });
 select undef, undef, undef, 1.1;