Fixes #4758

See https://github.com/Baystation12/Baystation12/issues/4758.

Fixed issue where removing the power cell would prevent certain checks on robot components. 
Also cleaned up /mob/living/silicon/robot/proc/use_power(), moved code related to status for better SRP. Added a line to the examine text to hint that the borg can still move without power. 
Sorry for all of this being in a single commit, things got screwed up with git.