Remove references to unused GN files and flags. (flutter/engine#2998)

* Remove references to unused GN files and flags.
* Fix Linux build.

engine/src/flutter/skia/BUILD.gn

@@ -13,8 +13,8 @@ group("skia") {
 } else {
 
 import("//build/config/features.gni")
-import("//build/config/ui.gni")
 import("//testing/test.gni")
+
 if (current_cpu == "arm" || current_cpu == "arm64") {
   import("//build/config/arm.gni")
 }
@@ -465,9 +465,6 @@ component("skia") {
       "//build/config/linux:fontconfig",
       "//build/config/linux:freetype2",
     ]
-    if (use_pango) {
-      configs += [ "//build/config/linux:pangocairo" ]
-    }
     deps += [ "//third_party/icu:icuuc" ]
   }
 

engine/src/flutter/tools/gn

@@ -64,7 +64,6 @@ def to_gn_args(args):
           # Always use AOT on iOS devices until the interpreter stabilizes
           aot = True
     else:
-      gn_args['use_aura'] = False
       gn_args['use_system_harfbuzz'] = False
       aot = False