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?

Inspect the Makefile's lint target and Bundletester's explicit charm-proof invocation. Confirm that lint currently runs proof redundantly and that removing that invocation leaves Bundletester responsible for proof. Done means the lint target no longer calls charm-proof while the existing lint flow remains intact.

Written by the indexing model from the issue text.