Revert "lowmemorykiller: don't unregister notifier from atomic context"

This reverts commit fa4af001353dc4665b90e0e301777964bb71f18b.
Revert "staging: android: lowmemorykiller: Don't wait more than one second fo…"

This reverts commit 6e1bd9951264542d6fb8d2814fe2289eb3e3eb5f.