Remove unneeded -Wno-deprecated-register flag

Test: m checkbuild
Change-Id: I030a66b8a484673caf3a96a844dc26954e08071a
diff --git a/cc/config/clang.go b/cc/config/clang.go
index 4862e05..d0d199b 100644
--- a/cc/config/clang.go
+++ b/cc/config/clang.go
@@ -127,7 +127,6 @@
 		"-Wno-zero-as-null-pointer-constant",
 
 		// Warnings from clang-7.0
-		"-Wno-deprecated-register",
 		"-Wno-sign-compare",
 
 		// Warnings from clang-8.0