Stop using public_deps to depend on libyuv.

A lot of WebRTC targets were depending on //third_party/libyuv using
public_deps instead of deps. This causes issues because a the
inclusion of libyuv headers is not declared to the build system and
this creates hidden dependencies that put the modularity of the project
at risk.

Bug: webrtc:8603
Change-Id: Ide0ceb84eb5640ae664dc782f3a722b55c3b601a
No-Try: True
Reviewed-on: https://webrtc-review.googlesource.com/28120
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Magnus Flodman <mflodman@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21039}

modules/video_processing/BUILD.gn

@@ -26,6 +26,7 @@ rtc_static_library("video_processing") {
 
   deps = [
     ":denoiser_filter",
+    "$rtc_libyuv_dir",
     "..:module_api",
     "../../common_audio",
     "../../common_video",