Remove support for legacy abstract declarations

runtime/vm/parser.cc

Index: runtime/vm/parser.cc
===================================================================
--- runtime/vm/parser.cc	(revision 17229)
+++ runtime/vm/parser.cc	(working copy)
@@ -31,8 +31,6 @@
             "Warning on legacy map literal syntax (single type argument)");
 DEFINE_FLAG(bool, strict_function_literals, false,
             "enforce new function literal rules");
-DEFINE_FLAG(bool, fail_legacy_abstract, false,
-            "error on explicit use of abstract on class members");
 
 static void CheckedModeHandler(bool value) {
   FLAG_enable_asserts = value;
@@ -2867,14 +2865,6 @@
   TRACE_PARSER("ParseClassMemberDefinition");
   MemberDesc member;
   current_member_ = &member;
-  if ((CurrentToken() == Token::kABSTRACT) &&
-      (LookaheadToken(1) != Token::kLPAREN)) {
-    if (FLAG_fail_legacy_abstract) {
-      ErrorMsg("illegal use of abstract");
-    }
-    ConsumeToken();
-    member.has_abstract = true;
-  }
   if ((CurrentToken() == Token::kEXTERNAL) &&
       (LookaheadToken(1) != Token::kLPAREN)) {
     ConsumeToken();