[cleanup] Remove stale TODO.

The StringEqual builtin handles two byte strings already.

Bug: v8:4913, v8:6365, v8:6371, v8:6936, v8:7022
Change-Id: I6f5a3999ccdce8e9bfcece6e94362c15183bbd8c
Reviewed-on: https://chromium-review.googlesource.com/778883Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49473}

src/builtins/builtins-string-gen.cc

@@ -189,7 +189,6 @@ void StringBuiltinsAssembler::GenerateStringEqual(Node* context, Node* left,
     // Try to unwrap indirect strings, restart the above attempt on success.
     MaybeDerefIndirectStrings(&var_left, lhs_instance_type, &var_right,
                               rhs_instance_type, &restart);
-    // TODO(bmeurer): Add support for two byte string equality checks.
 
     TailCallRuntime(Runtime::kStringEqual, context, lhs, rhs);
   }