Reduce end session delay for default IVibratorManager

Reduce fake delay for default implementation of HAL service
IVibratorManager to avoid flakiness in VTS tests.

The tests allow for a timeout of 100ms for ending a vibration session,
and the fake delay was too high at 50ms.

Change-Id: I519f73a477494cc0823249ca16c0925f22134dfb
Fix: 379204591
Flag: EXEMPT update default HAL implementation
Test: VtsHalVibratorManagerTargetTest