I believe this should be `if isKobo()`, or better yet that the entire
block should be moved to `KoboPowerD:init()` because afaik that is the
only platform where the system doesn't provide trustworthy frontlight
information. But to be absolutely sure that I don't break anything (and I
don't want to spend any time on this atm) I'm temporarily excluding only
Android where this behavior is known to be problematic.
See discussion in https://github.com/koreader/koreader/issues/3118#issuecomment-334995879
References #3118 (using keyword "references" because phrases like "possibly fixes"
result in GH autoclose).
