Clean up GN template code.

chrome/third_party/chromevox/BUILD.gn

 # Copyright 2014 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.
 
-if (is_chromeos) {
-  import("//chrome/browser/resources/chromeos/chromevox/chromevox.gni")
+assert(is_chromeos)
 
-  chromevox_out_dir = "$root_out_dir/resources/chromeos/chromevox"
+chromevox_out_dir = "$root_out_dir/resources/chromeos/chromevox"
 
-  group("chromevox_third_party_resources") {
-    deps = [
-      ":chromevox_third_party_background_resources",
-      ":chromevox_third_party_injected_resources",
-    ]
-  }
+group("chromevox_third_party_resources") {
+  deps = [
+    ":chromevox_third_party_background_resources",
+    ":chromevox_third_party_injected_resources",
+  ]
+}
 
-  copy("chromevox_third_party_background_resources") {
-    sources = [
-      "chromevox/background/chrome_shared2.css",
-      "chromevox/background/options.css",
-      "chromevox/background/options_widgets.css",
-    ]
-    outputs = [
-      "$chromevox_out_dir/chromevox/background/{{source_file_part}}",
-    ]
-  }
+copy("chromevox_third_party_background_resources") {
+  sources = [
+    "chromevox/background/chrome_shared2.css",
+    "chromevox/background/options.css",
+    "chromevox/background/options_widgets.css",
+  ]
+  outputs = [
+    "$chromevox_out_dir/chromevox/background/{{source_file_part}}",
+  ]
+}
 
-  copy("chromevox_third_party_injected_resources") {
-    sources = [
-      "chromevox/injected/mathjax.js",
-      "chromevox/injected/mathjax_external_util.js",
-    ]
-    outputs = [
-      "$chromevox_out_dir/chromevox/injected/{{source_file_part}}",
-    ]
-  }
+copy("chromevox_third_party_injected_resources") {
+  sources = [
+    "chromevox/injected/mathjax.js",
+    "chromevox/injected/mathjax_external_util.js",
+  ]
+  outputs = [
+    "$chromevox_out_dir/chromevox/injected/{{source_file_part}}",
+  ]
 }