internal/impl: remove blocking TODO

This TODO doesn't need to be addressed for v2 release.
Addressing this now would probably need to go through global testing,
which is not worth the effort now.

Change-Id: I44bf45e077c00e9a6462905193efb0bce41e9dd2
Reviewed-on: https://go-review.googlesource.com/c/protobuf/+/220345
Reviewed-by: Damien Neil <dneil@google.com>
diff --git a/internal/impl/message_reflect.go b/internal/impl/message_reflect.go
index cff9067..f5f7f2b 100644
--- a/internal/impl/message_reflect.go
+++ b/internal/impl/message_reflect.go
@@ -330,7 +330,7 @@
 
 	if fd.IsExtension() {
 		if fd.ContainingMessage().FullName() != mi.Desc.FullName() {
-			// TODO(blocks): Should this be exact containing message descriptor match?
+			// TODO: Should this be exact containing message descriptor match?
 			panic("mismatching containing message")
 		}
 		if !mi.Desc.ExtensionRanges().Has(fd.Number()) {