arcvm: Remove unused method ArcVmClientAdapterTest::GetTempDir()

BUG=None
TEST=try

Change-Id: I167add5ffa3833387b0f246f6ffc497e80959209
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2083050
Commit-Queue: Yury Khmel <khmel@chromium.org>
Auto-Submit: Yusuke Sato <yusukes@chromium.org>
Reviewed-by: Yury Khmel <khmel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#746042}

components/arc/session/arc_vm_client_adapter_unittest.cc

@@ -280,7 +280,6 @@ class ArcVmClientAdapterTest : public testing::Test,
 
   base::RunLoop* run_loop() { return run_loop_.get(); }
   ArcClientAdapter* adapter() { return adapter_.get(); }
-  const base::FilePath& GetTempDir() const { return dir_.GetPath(); }
 
   bool arc_instance_stopped_called() const {
     return arc_instance_stopped_called_;