Request lmkd to purge its list of pids after establishing connection

lmkd keeps a list of pids registered by ActivityManager, however on rare
occasions when framework restarts and lmkd survives that list has to be
purged. Request lmkd to clear its pid list immediately after establishing
connection to it.

Bug: 116801366
Test: locally by killing zygote process
Change-Id: Id8c81e0cb0c4cf03b8faa0add5a9514fd3cd0c0c
Signed-off-by: Suren Baghdasaryan <surenb@google.com>