Removing $rtc_libyuv_dir and removing useless dependencies on libyuv.

This CL removes the following GN variables: rtc_build_libyuv,
rtc_libyuv_dir (as requested in webrtc:7906).
It also removes some unneeded dependencies on //third_party/libyuv.

WebRTC targets were using public_deps to depend on //third_party/libyuv
and this created a build graph where targets that were depending on
//third_party/libyuv were not declaring the dependency to GN because
they were somehow getting it from another target that was exposing
//third_party/libyuv header files even if it wasn't directly depending
on it.

Bug: webrtc:8605, webrtc:7906
Change-Id: If71f7988fd80421dc2ad887cf94c2ac66366c3fb
Reviewed-on: https://webrtc-review.googlesource.com/32201
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21275}
diff --git a/sdk/BUILD.gn b/sdk/BUILD.gn
index 9161a29..d8d4b7b 100644
--- a/sdk/BUILD.gn
+++ b/sdk/BUILD.gn
@@ -134,7 +134,6 @@
 
       deps = [
         ":common_objc",
-        "$rtc_libyuv_dir",
         "../api:libjingle_peerconnection_api",
         "../api:video_frame_api",
         "../api:video_frame_api_i420",
@@ -142,6 +141,7 @@
         "../media:rtc_media_base",
         "../rtc_base:checks",
         "../rtc_base:rtc_base",
+        "//third_party/libyuv",
       ]
 
       configs += [ "..:common_objc" ]
@@ -305,7 +305,6 @@
         ":corevideoframebuffer_objc",
         ":peerconnectionfactory_objc",
         ":video_objc",
-        "$rtc_libyuv_dir",
         "../api:video_frame_api",
         "../media:rtc_media_base",
         "../pc:libjingle_peerconnection",
@@ -773,11 +772,11 @@
       ]
 
       deps = [
-        "$rtc_libyuv_dir",
         "../api:video_frame_api_i420",
         "../common_video",
         "../rtc_base:checks",
         "../rtc_base:rtc_base_approved",
+        "//third_party/libyuv",
       ]
 
       if (!build_with_chromium && is_clang) {
@@ -829,7 +828,6 @@
         ":video_objc",
         ":video_toolbox_cc",
         ":videotracksource_objc",
-        "$rtc_libyuv_dir",
         "../api/video_codecs:video_codecs_api",
         "../common_video",
         "../media:rtc_media",
@@ -840,6 +838,7 @@
         "../rtc_base:checks",
         "../rtc_base:rtc_base_approved",
         "../system_wrappers",
+        "//third_party/libyuv",
       ]
 
       libs = [