automatically detect vendored buildkit version

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

Makefile

@@ -31,14 +31,7 @@ shellcheck:
 	shellcheck ./universe/*.bats ./universe/*.bash
 
 .PHONY: lint
-lint: shellcheck cuelint golint check-buildkit-version docslint
-
-.PHONY: check-buildkit-version
-check-buildkit-version:
-	@test \
-		"$(shell grep buildkit ./go.mod | cut -d' ' -f2)" = \
-		"$(shell grep ' = "v' ./util/buildkitd/buildkitd.go | sed -E 's/^.*version.*=.*\"(v.*)\"/\1/' )" \
-		|| { echo buildkit version mismatch go.mod != util/buildkitd/buildkitd.go ; exit 1; }
+lint: shellcheck cuelint golint docslint
 
 .PHONY: integration
 integration: core-integration universe-test