Remove GN group backward-compat code.

tools/gn/group_target_generator.cc

Index: tools/gn/group_target_generator.cc
diff --git a/tools/gn/group_target_generator.cc b/tools/gn/group_target_generator.cc
index 707d275ef9234fcba8e0565627d61e3df743ed9d..2c427f4cc49ab1b5f9a9d5f2f3fb10bda8a5d935 100644
--- a/tools/gn/group_target_generator.cc
+++ b/tools/gn/group_target_generator.cc
@@ -22,13 +22,4 @@ void GroupTargetGenerator::DoRun() {
   target_->set_output_type(Target::GROUP);
   // Groups only have the default types filled in by the target generator
   // base class.
-
-  // Before there was a deps/public_deps split, a group acted like all deps
-  // are public. During a transition period, if public_deps is not defined,
-  // treat all deps as public. This should be removed and existing groups
-  // updated to use "public_deps" when needed.
-  if (scope_->GetValue(variables::kDeps, false) &&
-      !scope_->GetValue(variables::kPublicDeps, false)) {
-    std::swap(target_->private_deps(), target_->public_deps());
-  }
 }