Fix race condition in `multiplePoliciesSet_dpcRemoved_removesPolicies` Bug: 320787883 Test: btest a.d.c.DeviceManagementCoexistenceTest#multiplePoliciesSet_dpcRemoved_removesPolicies (cherry picked from https://googleplex-android-review.googlesource.com/q/commit:d105a990b59a531e97e7c50c4bc763c84887ef8c) Merged-In: If2fc7efe9d074c1cb66cbb8ee1b6fab542c52eeb Change-Id: If2fc7efe9d074c1cb66cbb8ee1b6fab542c52eeb