Enable deprecated-enum-enum-conversion warning

Test: presubmit
Bug: 153746563
Change-Id: Id54685056c4e6280dd2962527e11fb7efb840660
diff --git a/cc/config/global.go b/cc/config/global.go
index a4627b2..dfb9a66 100644
--- a/cc/config/global.go
+++ b/cc/config/global.go
@@ -222,7 +222,6 @@
 		"-Wno-misleading-indentation",               // http://b/153746954
 		"-Wno-zero-as-null-pointer-constant",        // http://b/68236239
 		"-Wno-deprecated-anon-enum-enum-conversion", // http://b/153746485
-		"-Wno-deprecated-enum-enum-conversion",      // http://b/153746563
 		"-Wno-string-compare",                       // http://b/153764102
 		"-Wno-pessimizing-move",                     // http://b/154270751
 		// New warnings to be fixed after clang-r399163