Remove '-Wno-return-std-move-in-c++11' flag

This flag is no longer needed.

Test: presubmit
Change-Id: I9718ea1d448a6f598e6da61c3b30a0c9470d9c08
diff --git a/cc/config/clang.go b/cc/config/clang.go
index 1f169e4..3636ae9 100644
--- a/cc/config/clang.go
+++ b/cc/config/clang.go
@@ -171,9 +171,6 @@
 		// Disable c++98-specific warning since Android is not concerned with C++98
 		// compatibility.
 		"-Wno-c++98-compat-extra-semi",
-
-		// Disable this warning because we don't care about behavior with older compilers.
-		"-Wno-return-std-move-in-c++11",
 	}, " "))
 
 	// Extra cflags for projects under external/ directory to disable warnings that are infeasible