Remove generation of AUTHORS

This is unused, and currently breaks the spellcheck rule. I was
going to just skip spell checking it, but it seems easier to remove
the file generation instead.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

Makefile

@@ -45,10 +45,7 @@ PKGS ?= $(shell go list -tags "${NOTARY_BUILDTAGS}" ./... | grep -v /vendor/ | t
 .DELETE_ON_ERROR: cover
 .DEFAULT: default
 
-all: AUTHORS clean lint build test binaries
-
-AUTHORS: .git/HEAD
-	git log --format='%aN <%aE>' | sort -fu > $@
+all: clean lint build test binaries
 
 # This only needs to be generated by hand when cutting full releases.
 version/version.go: