Change 'chromium_builder_tests' to be empty in GN builds.

BUILD.gn

Index: BUILD.gn
diff --git a/BUILD.gn b/BUILD.gn
index 0a7fe5675d940c85d2fbaf89383c8019eed5e45c..84e1a54b64b9e2eee51a62685f796110a917424d 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -85,14 +85,14 @@ group("All") {
 }
 
 # TODO(GYP_GONE): This target exists for compatibility with GYP for the
-# builders. For now, this builds everything. We should decide if we want to
-# build less.
+# builders that specify targets in the recipes directly.
+# Ideally it should not exist, and the builders should be specifying
+# more specific targets (or 'All') via the source-side
+# //testing/buildbot/*.json files. We should simply delete this target
+# and update any recipes that are using it.
 group("chromium_builder_tests") {
   testonly = true
-
-  deps = [
-    ":All",
-  ]
+  deps = []
 }
 
 if (is_chromeos) {