Update GN build files for new prefs location.

base/BUILD.gn

Index: base/BUILD.gn
diff --git a/base/BUILD.gn b/base/BUILD.gn
index cf0d5a1ce313daa6fc0d4f9d9a6a80f422e8f772..60821ee36313f4ba466002833083e35902768655 100644
--- a/base/BUILD.gn
+++ b/base/BUILD.gn
@@ -1465,20 +1465,6 @@ if (is_ios || is_android || is_win || (is_linux && !is_chromeos)) {
   }
 }
 
-# TODO(brettw) remove these forwarding targets when all references to prefs are
-# updated to point to components.
-group("prefs") {
-  public_deps = [
-    "//components/prefs",
-  ]
-}
-group("prefs_test_support") {
-  testonly = true
-  public_deps = [
-    "//components/prefs:test_support",
-  ]
-}
-
 source_set("message_loop_tests") {
   testonly = true
   sources = [