Revert of Loosening the coupling between WebRTC and //third_party/protobuf

webrtc/base/BUILD.gn

Index: webrtc/base/BUILD.gn
diff --git a/webrtc/base/BUILD.gn b/webrtc/base/BUILD.gn
index dd3b45628c7b4b5c3d5e1ffe900717188f1ad645..3d0a3f42f1c113680b68e401bc3b9ae6f7a79628 100644
--- a/webrtc/base/BUILD.gn
+++ b/webrtc/base/BUILD.gn
@@ -76,17 +76,6 @@
     assert(rtc_ssl_root != "",
            "You must specify rtc_ssl_root when rtc_build_ssl==0.")
     include_dirs = [ rtc_ssl_root ]
-  }
-}
-
-source_set("protobuf_utils") {
-  sources = [
-    "protobuf_utils.h",
-  ]
-  if (rtc_enable_protobuf) {
-    public_deps = [
-      "//third_party/protobuf:protobuf_lite",
-    ]
   }
 }