Remove support for operator negate and replace occurrences with unary

lib/compiler/implementation/scanner/parser.dart

Index: lib/compiler/implementation/scanner/parser.dart
diff --git a/lib/compiler/implementation/scanner/parser.dart b/lib/compiler/implementation/scanner/parser.dart
index 695332e50c669095db0ea4fefdd59a71a9273d63..b2b0f548c4ca571a0d8cc3459de555b02349a854 100644
--- a/lib/compiler/implementation/scanner/parser.dart
+++ b/lib/compiler/implementation/scanner/parser.dart
@@ -800,9 +800,7 @@ class Parser {
 
   Token parseOperatorName(Token token) {
     assert(optional('operator', token));
-    if (isUserDefinableOperator(token.next.stringValue)
-        // TODO(ahe): Remove negate.
-        || token.next.value == const SourceString("negate")) {
+    if (isUserDefinableOperator(token.next.stringValue)) {
       Token operator = token;
       token = token.next;
       listener.handleOperatorName(operator, token);