Fix SynchedDeviceConfigTest flakiness

We remove the test related to the chance of updating the compile
time value which is now not possible. That test also contained
a synchronisation problem due to the use of two different
implementations of DeviceConfigListener receiving updates at the
wrong time.

Fix: 287273345
Test: Run `atest SynchedDeviceConfigTests`

Change-Id: I22c3e19cd935063e1b956df4dbed5d194368ce4c