Enable H104, F841 hacking rule and fix violations

This change enables hacking check H104 and F841, and fixes all
violations.

[H104]    Files with no code shouldn’t contain any license header nor
          comments, and must be left completely empty.
[F841]    local variable name is assigned to but never used

Change-Id: If7fcb737d121fd13b2b103d63f5f26dfaa79c59b
Merge "Enable H104, F841 hacking rule and fix violations"