Remove unnecessary mocking in tearDown

The setup for the mocking object will be reset when each test
finishs the test. Reset the mocking value is actually no-op
but cause possible threading issue in Mokito.

Bug: 278979735
Test: atest com.android.server.connectivity.VpnTest \
      --rerun-until-failure 100
Change-Id: Ib8c3813e5dbcc9b7432a5548766d63e400b4ed0e
1 file changed