Set account just in time instead of via constructor

We were passing Android contact storage implementation details all
throughout the PBAP Client OBEX code. The VCard object has a setAccount
function we can use instead, so we con't need to do this. Storage will
now just apply the given account at storage time.

Flag: EXEMPT, trivial mechanical refactor
Bug: 393095177
Test: atest com.android.bluetooth.pbapclient
Change-Id: I66c0244de5b89de719477ed7bde30457edaa76cc