[ast] Remove dead AstValueFactory::NewStringList method declaration

Change-Id: I6288e295dd403be45cb2e4a648ac50c8f1376b73
Reviewed-on: https://chromium-review.googlesource.com/734481Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48849}

src/ast/ast-value-factory.h

@@ -429,7 +429,6 @@ class AstValueFactory {
   const AstValue* NewSmi(uint32_t number);
   V8_EXPORT_PRIVATE const AstValue* NewBigInt(const char* number);
   const AstValue* NewBoolean(bool b);
-  const AstValue* NewStringList(ZoneList<const AstRawString*>* strings);
   const AstValue* NewNull();
   const AstValue* NewUndefined();
   const AstValue* NewTheHole();