Fix null deref in sensors 2.0 VTS teardown

Avoid attempting to clean up resources that were never initialized, e.g.
if the target device doesn't support the version of the HAL in question.

Fixes: 134911861
Test: run VtsHalSensorsV2_0Target on device that only supports HAL v1.0
Change-Id: I6b529fae13b1347d533a19e04f1c7748bcda961b