Stop using public_deps in stats.

Bug: None
Change-Id: Id73fd4e4f83f2942cb1b394908ccc729933977cf
Reviewed-on: https://webrtc-review.googlesource.com/29020
Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21044}

stats/BUILD.gn

@@ -9,7 +9,7 @@
 import("../webrtc.gni")
 
 group("stats") {
-  public_deps = [
+  deps = [
     ":rtc_stats",
   ]
 }