Fix lock contention in Attention

Call checkAttention() sits in the critical path inside the PowerManager.
To avoid the lock contention, don't call into the PackageManager.
Specifically, checking the configuration with the PackageManager is
redundant since it's already done by SystemServer - it won't start the
AttentionManagerService if it's not configured.

Bug: 169427927
Test: manually
Change-Id: I46ca7a6ce01d2229521f1fe12a80440024465c67