[parser] Remove outdated comment about trivial expression parsing

Change-Id: I403a6c5124f560d47a3b5d54d79bf54563207c1e
Reviewed-on: https://chromium-review.googlesource.com/c/1296269Reviewed-by: Marja Hölttä <marja@chromium.org>
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56888}

src/parsing/parser-base.h

@@ -2724,8 +2724,6 @@ ParserBase<Impl>::ParseAssignmentExpression(bool accept_IN, bool* ok) {
   bool parenthesized_formals =
       (is_async ? PeekAhead() : peek()) == Token::LPAREN;
 
-  // Parse a simple, faster sub-grammar (primary expression) if it's evident
-  // that we have only a trivial expression to parse.
   ExpressionT expression = ParseConditionalExpression(accept_IN, CHECK_OK);
 
   if (peek() == Token::ARROW) {