Use Slog instead of EventLogger in MediaSessionStack

Logs that previously appeared in dumpsys now appear in
system logs.

For testing, get system logs live with logcat, for example:
adb logcat MediaSessionStack:I *:S
or generate a bug report, for example:
adb bugreport
then browse the file with the Android Bug Tool UI at
go/abt-web

Bug: 259705163
Test: manually
Change-Id: I57d8ab1e1fc9b8a68e94bf8895fd128d1545c45e