MAP: toward removing StaticGuardedByInstance error

remove static getRemoteDevice method.

This will never outerlive the mapservice (plus the device is set to null
when the service close)

Bug: 344658662
Test: m Bluetooth
Flag: exempt refactor
Change-Id: I9a58d56a3cc38d3c27e1fe4e2441efc4d05b2e1a