GN, GYP: Remove -Wno-incompatible-pointer-types flag for building NSS.

net/third_party/nss/ssl/BUILD.gn

Index: net/third_party/nss/ssl/BUILD.gn
diff --git a/net/third_party/nss/ssl/BUILD.gn b/net/third_party/nss/ssl/BUILD.gn
index 7c4590f2e0edc1398b4bf7b1ab140a8e940cad25..b8fe40fc4087d24d6e6de7749df530c3a689bf29 100644
--- a/net/third_party/nss/ssl/BUILD.gn
+++ b/net/third_party/nss/ssl/BUILD.gn
@@ -130,14 +130,6 @@ component("libssl") {
     ]
   }
 
-  if (is_clang) {
-    cflags += [
-      # See http://crbug.com/138571#c8. In short, sslsecur.c picks up the
-      # system's cert.h because cert.h isn't in chromium's repo.
-      "-Wno-incompatible-pointer-types",
-    ]
-  }
-
   if (is_debug) {
     defines += [ "DEBUG" ]
   }