Tidy up RulesManagerService code

1) Remove error handling TODO; no obvious issues.
2) Avoid avoid a NullPointerException in dumpsys code when current
state cannot be read.
3) Remove unnecessary public modifier.

Bug: 31008728
Test: make
Change-Id: Iab5fae74b74f54bf9d19410f0f4c9ed94365a162
(cherry picked from commit a47c3637)