[Chromecast] Remove redundant build assert.

chromecast/chromecast.gni

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import("//build/config/chromecast_build.gni")
 
 # This args block should contain arguments used within the //chromecast
 # directory. Arguments which are used in other Chrome components should
 # be instead declared in //build/config/chromecast_build.gni.
 declare_args() {
@@ skipping 28 matching lines @@
 
 # This is the release version, which takes the form <major>.<minor>. Internal
 # builds will read the value from an internal file containing this value as a
 # string. Public builds, lacking this file, will set a dummy value.
 if (chromecast_branding == "public") {
   cast_build_release = "eng." + getenv("USER")
 } else {
   cast_build_release =
       read_file("//chromecast/internal/build/cast_build_release", "trim string")
 }
-
-# Assistant shall only be enabled on audio-only builds.
-assert(!enable_assistant || is_cast_audio_only,
-       "Assistant is only available on audio devices.")