git: drop auto coverletter
git: drop auto coverletter

Sending patches over email is not my most common use of this. Drop
coverLetter from config and add it manually when necessary.

Signed-off-by: Liam Beguin <ac8b122174024ef5e58ca7d6d989651e9bbfc948@gmail.com>

Liambeguin/dotfiles,Liambeguin/dotfiles