[temp fix] Stop broadcasting onProcessStarted.

This fixes system server crashes caused by race condition between
multiple concurrent broadcasts to IProcessObserver, likely caused by the
recently added code for broadcasting onProcessStarted. The fix removes
the newly added code.

A subsequent change will add back the implementation with proper
concurrency protection.

Test: m
Bug: 323925686
Change-Id: I3cb1df12c5146a4914c5082790f71e0c4b17e4fe