Kill AppZygote when a package is removed with DONT_KILL.

When a package is being removed with DONT_KILL, we should still
kill any App Zygote instances that may be running, since they
are referring to old code, and will not be able to spawn any
new processes anyway. New service requests will automatically
spawn a new app zygote process.

Bug: 144095172
Test: Manual test with Chrome
Change-Id: I2e5de604312bb7739ba3ef6abb63d534c74522f2