Revert "[parser] allow ASI when "await" or "yield" follows "let""

This reverts commit 96698b55.

Reason for revert: This patch was correct when it landed, but later,
the spec was changed to V8's old behavior in
https://github.com/tc39/ecma262/pull/885 .

Original change's description:
> [parser] allow ASI when "await" or "yield" follows "let"
> 
> Per https://github.com/tc39/test262/pull/956, André believes that ASI
> should be permitted in these situations.
> 
> BUG=
> R=​marja@chromium.org, adamk@chromium.org, littledan@chromium.org
> 
> Change-Id: I5602d8a507576607750ffa9e873e1bfa53dd3523
> Reviewed-on: https://chromium-review.googlesource.com/472568
> Reviewed-by: Marja Hölttä <marja@chromium.org>
> Commit-Queue: Caitlin Potter <caitp@igalia.com>
> Cr-Commit-Position: refs/heads/master@{#44585}

TBR=adamk@chromium.org,marja@chromium.org,littledan@chromium.org,caitp@igalia.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I2c5bf709867da539ccd4cd82f3be98c8a0301f31
Reviewed-on: https://chromium-review.googlesource.com/553617Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Daniel Ehrenberg <littledan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46317}

src/parsing/parser-base.h

@@ -4238,14 +4238,10 @@ bool ParserBase<Impl>::IsNextLetKeyword() {
                       // for those semantics to apply. This ensures that ASI is
                       // not honored when a LineTerminator separates the
                       // tokens.
+    case Token::YIELD:
+    case Token::AWAIT:
     case Token::ASYNC:
       return true;
-    case Token::AWAIT:
-      // In an async function, allow ASI between `let` and `yield`
-      return !is_async_function() || !scanner_->HasAnyLineTerminatorAfterNext();
-    case Token::YIELD:
-      // In an generator, allow ASI between `let` and `yield`
-      return !is_generator() || !scanner_->HasAnyLineTerminatorAfterNext();
     case Token::FUTURE_STRICT_RESERVED_WORD:
       return is_sloppy(language_mode());
     default:

test/message/let-asi-await-nonasync.js

-// Copyright 2017 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-var let = 0;
-function nonAsync() {
-  let
-  await 0;
-}

test/message/let-asi-await-nonasync.out

-*%(basename)s:8: SyntaxError: Unexpected number
-  await 0;
-        ^
-SyntaxError: Unexpected number

test/message/let-asi-yield-nongenerator.js

-// Copyright 2017 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-var let = 0;
-function nonGenerator() {
-  let
-  yield 0;
-}

test/message/let-asi-yield-nongenerator.out

-*%(basename)s:8: SyntaxError: Unexpected number
-  yield 0;
-        ^
-SyntaxError: Unexpected number

test/mjsunit/es6/generator-let-asi.js

-// Copyright 2017 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-var let = 0;
-function* generator() {
-  let
-  yield 0;
-}
-
-let it = generator();
-let {value, done} = it.next();
-assertEquals(0, value);
-assertEquals(false, done);

test/mjsunit/es8/async-let-asi.js

-// Copyright 2017 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-// Flags: --allow-natives-syntax
-
-var let = 0;
-async function asyncFn() {
-  let
-  await 0;
-  return 0;
-}
-
-asyncFn().then(value => {
-  assertEquals(0, value);
-}, error => {
-  assertUnreachable();
-}).catch(error => {
-  %AbortJS(String(error));
-});
-
-%RunMicrotasks();