Bug 1641091, part 1 - Remove the unused ContentChild::GetEventTargetFor. r=froydnj

This all is leftovers from Quantum DOM.

Differential Revision: https://phabricator.services.mozilla.com/D76982

dom/ipc/ContentChild.cpp

@@ -3279,11 +3279,6 @@ mozilla::ipc::IPCResult ContentChild::RecvRefreshScreens(
   return IPC_OK();
 }
 
-already_AddRefed<nsIEventTarget> ContentChild::GetEventTargetFor(
-    BrowserChild* aBrowserChild) {
-  return IToplevelProtocol::GetActorEventTarget(aBrowserChild);
-}
-
 mozilla::ipc::IPCResult ContentChild::RecvSetPluginList(
     const uint32_t& aPluginEpoch, nsTArray<plugins::PluginTag>&& aPluginTags,
     nsTArray<plugins::FakePluginTag>&& aFakePluginTags) {

dom/ipc/ContentChild.h

@@ -617,9 +617,6 @@ class ContentChild final : public PContentChild,
   nsresult AsyncOpenAnonymousTemporaryFile(
       const AnonymousTemporaryFileCallback& aCallback);
 
-  already_AddRefed<nsIEventTarget> GetEventTargetFor(
-      BrowserChild* aBrowserChild);
-
   mozilla::ipc::IPCResult RecvSetPluginList(
       const uint32_t& aPluginEpoch, nsTArray<PluginTag>&& aPluginTags,
       nsTArray<FakePluginTag>&& aFakePluginTags);