[parser] Delete misplaced const.

'const' type qualifier on return type has no effect and
produces compiler warnings.

BUG=

Review-Url: https://codereview.chromium.org/2751513004
Cr-Commit-Position: refs/heads/master@{#43839}

src/parsing/parser.h

@@ -206,7 +206,7 @@ class V8_EXPORT_PRIVATE Parser : public NON_EXPORTED_BASE(ParserBase<Parser>) {
     cached_parse_data_ = NULL;
   }
 
-  static bool const IsPreParser() { return false; }
+  static bool IsPreParser() { return false; }
 
   void ParseOnBackground(ParseInfo* info);
 

src/parsing/preparser.h

@@ -892,7 +892,7 @@ class PreParser : public ParserBase<PreParser> {
         track_unresolved_variables_(false),
         pending_error_handler_(pending_error_handler) {}
 
-  static bool const IsPreParser() { return true; }
+  static bool IsPreParser() { return true; }
 
   PreParserLogger* logger() { return &log_; }