Remove unused enable_chromevox_next.

build/config/features.gni

Index: build/config/features.gni
diff --git a/build/config/features.gni b/build/config/features.gni
index dee4632a13d8cde30c53709304723214624e977f..12870246417cf27e8dd2c78f4b0600c7041acb1a 100644
--- a/build/config/features.gni
+++ b/build/config/features.gni
@@ -71,12 +71,6 @@ declare_args() {
   # Whether or not to use external popup menu.
   use_external_popup_menu = is_android || is_mac
 }
-
-# Additional dependent variables -----------------------------------------------
-
-# Chrome OS: whether to also build the upcoming version of
-# ChromeVox, which can then be enabled via a command-line switch.
-enable_chromevox_next = false
 #
 # =============================================
 #   PLEASE DO NOT ADD MORE FLAGS TO THIS FILE