Remove unused friend decl from update_service_unittest.

Bug: 1105922
Change-Id: I3475c8848d9ed5af078db8eebac75e2021583dd7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2315801Reviewed-by: Joshua Pawlicki <waffles@chromium.org>
Commit-Queue: Sorin Jianu <sorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791246}

extensions/browser/updater/update_service_unittest.cc

@@ -137,7 +137,6 @@ class FakeUpdateClient : public update_client::UpdateClient {
   }
 
  protected:
-  friend class base::RefCounted<FakeUpdateClient>;
   ~FakeUpdateClient() override = default;
 
   std::vector<base::Optional<update_client::CrxComponent>> data_;