Remove use_aura build arg.

build/config/ui.gni

Index: build/config/ui.gni
diff --git a/build/config/ui.gni b/build/config/ui.gni
index 1d0a3f092af35d40e50b783a1b0abab26e3b1a71..a9ece25ee258710eefbc5db68c4a045b6a94d877 100644
--- a/build/config/ui.gni
+++ b/build/config/ui.gni
@@ -15,20 +15,12 @@ declare_args() {
   # Indicates if Ozone is enabled. Ozone is a low-level library layer for Linux
   # that does not require X11.
   use_ozone = false
-
-  # Indicates if Aura is enabled. Aura is a low-level windowing library, sort
-  # of a replacement for GDI or GTK.
-  use_aura = is_linux
 }
 
 # Additional dependent variables -----------------------------------------------
 #
 # These variables depend on other variables and can't be set externally.
 
-# Use GPU accelerated cross process image transport by default on linux builds
-# with the Aura window manager.
-ui_compositor_image_transport = use_aura && is_linux
-
 # Indicates if the UI toolkit depends on X11.
 use_x11 = is_linux && !use_ozone