Remove obsolete/infeasible TODOs

(a) Clean up LogEvent::parseBuffer - having those variables be member
variables really helps with code readability.

(b) Don't hold locks when writing to pipe within ShellSubscriber -
ag/150969574 describes why holding a lock is necessary.

Test: m
Bug: 150312423 (allows this bug to be marked as obsolete)
Change-Id: I4903de1dc87a552932b70e5975a7cde91df05b3b