Moving no_op_function.cc out of webrtc/build

BUG=webrtc:7030

Review-Url: https://codereview.webrtc.org/2645223003
Cr-Commit-Position: refs/heads/master@{#16246}

webrtc/BUILD.gn

@@ -229,7 +229,7 @@ if (!build_with_chromium) {
     sources = [
       # TODO(kjellander): Remove this whenever possible. GN's static_library
       # target type requires at least one object to avoid errors linking.
-      "build/no_op_function.cc",
+      "no_op_function.cc",
 
       # TODO(ossu): Keep this here until donwstream projects have updated.
       # http://bugs.webrtc.org/6716