Remove some bogus type promotion code.

pkg/front_end/testcases/inference/type_promotion_not_and_not.dart.strong.expect

Index: pkg/front_end/testcases/inference/type_promotion_not_and_not.dart.strong.expect
diff --git a/pkg/front_end/testcases/inference/type_promotion_not_and_not.dart.strong.expect b/pkg/front_end/testcases/inference/type_promotion_not_and_not.dart.strong.expect
new file mode 100644
index 0000000000000000000000000000000000000000..c1b36d920a93627e7bb924b801a9b31090e99f62
--- /dev/null
+++ b/pkg/front_end/testcases/inference/type_promotion_not_and_not.dart.strong.expect
@@ -0,0 +1,10 @@
+library test;
+import self as self;
+import "dart:core" as core;
+
+static method f(core::Object x) → void {
+  if(!(x is core::int) && !(x is core::String)) {
+    core::print(x);
+  }
+}
+static method main() → dynamic {}