[Chromecast] remove some unused deps.

Bug: internal b/146428609
Test: on device
Change-Id: I7de4306f2836d05c2686379ea0face5b4a3f53bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1979101
Reviewed-by: Sergey Volk <servolk@chromium.org>
Commit-Queue: Gaofeng Huang <gfhuang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726880}

diff --git a/chromecast/chromecast.gni b/chromecast/chromecast.gni
index 6ea014bd..faa8dff 100644
--- a/chromecast/chromecast.gni
+++ b/chromecast/chromecast.gni

@@ -166,7 +166,9 @@
   cast_locales -= android_only_chrome_locales - [ "zh-HK" ]
 }
 
-enable_chromecast_extensions = enable_extensions
+declare_args() {
+  enable_chromecast_extensions = enable_extensions
+}
 
 # Use Chromecast CDMs for protected content. Some Android platforms use
 # MediaDrm for CDM support.