make lint has redundant behavior

Bundletester explicitly calls charm-proof, so we really don't need to call it in the makefile during lint.

background info:

having this added to the makefile is redundant, and necessitates me to fork the makefile in my upper layer if I wish to remove this behavior. Charm-tools hasn't been bumped in quite a while and charms leveraging new features will consistently fail when using keywords like:
- terms
- resources

I feel like having lint fail consistently, when proof has already failed, raises red herrings.

Can we remove the proof step from the lint target to stop the redundancy?