Remove //modules/video_coding:nack_module from API.

Bug: None
Change-Id: I8e6cc61ae8406993909d0ab97896ccbaa89349c1
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/176082
Commit-Queue: Tommi <tommi@webrtc.org>
Reviewed-by: Tommi <tommi@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31349}
diff --git a/modules/video_coding/BUILD.gn b/modules/video_coding/BUILD.gn
index b084577..2d0a6b3 100644
--- a/modules/video_coding/BUILD.gn
+++ b/modules/video_coding/BUILD.gn
@@ -68,7 +68,6 @@
 }
 
 rtc_library("nack_module") {
-  visibility = [ "*" ]
   sources = [
     "histogram.cc",
     "histogram.h",