PBAP: Get ready to reload contacts on user switch

PbapService:
- Use ACTION string constants to avoid null checks
- Remove the parameters for savePbapParams
- Remove unnecessary try blocks

PbapUtils:
- Reduce the scope of local variables
- Rename static variables s<VariableName>
- Remove dead code
- Avoid a null-pointer exception in nameTmp mName comparison

Bug: 72435402
Test: runtest bluetooth
      Connect and disconnect to a car kit
Change-Id: I15531abfe7eb9c76788eed301f9356d60c7a6829