PlatformSensorAndProviderLinuxTest: Remove TearDown() override.

The only remaining code there was a call to RunLoop::RunUntilIdle() that had
been present since this file was added to the tree.

Whatever it was waiting for seems to have been fixed since then though, as
removing the call still allows all tests to pass, and we get no subsequent
crashes.

Change-Id: Ie1141f7870d89ed4f1ea89015e4ce2b4b67acc36
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2216223
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Auto-Submit: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Reviewed-by: Reilly Grant <reillyg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#772295}

services/device/generic_sensor/platform_sensor_and_provider_unittest_linux.cc

@@ -200,8 +200,6 @@ class PlatformSensorAndProviderLinuxTest : public ::testing::Test {
         provider_->weak_ptr_factory_.GetWeakPtr()));
   }
 
-  void TearDown() override { base::RunLoop().RunUntilIdle(); }
-
  protected:
   MockSensorDeviceManager* mock_sensor_device_manager() const {
     return static_cast<MockSensorDeviceManager*>(