Revert "Enable syntax-only support for generic functions by default."

pkg/compiler/lib/src/diagnostics/messages.dart

Index: pkg/compiler/lib/src/diagnostics/messages.dart
diff --git a/pkg/compiler/lib/src/diagnostics/messages.dart b/pkg/compiler/lib/src/diagnostics/messages.dart
index a65c6ef83a9976f467c5ab8bee0927a76c02332a..a5e40038e8c72379e1bf11898f6427b058c34623 100644
--- a/pkg/compiler/lib/src/diagnostics/messages.dart
+++ b/pkg/compiler/lib/src/diagnostics/messages.dart
@@ -1221,6 +1221,7 @@ void main() => new C().m(null);
       MessageKind.TYPE_VARIABLE_FROM_METHOD_NOT_REIFIED: const MessageTemplate(
           MessageKind.TYPE_VARIABLE_FROM_METHOD_NOT_REIFIED,
           "Method type variables do not have a runtime value.",
+          options: const ["--generic-method-syntax"],
           howToFix: "Try using the upper bound of the type variable, "
               "or refactor the code to avoid needing this runtime value.",
           examples: const [
@@ -1242,6 +1243,7 @@ main() => f<int>(42);
       const MessageTemplate(
           MessageKind.TYPE_VARIABLE_FROM_METHOD_CONSIDERED_DYNAMIC,
           "Method type variables are treated as `dynamic` in `as` expressions.",
+          options: const ["--generic-method-syntax"],
           howToFix: "Try using the upper bound of the type variable, or check "
               "that the blind success of the test does not introduce bugs.",
           examples: const [