Remove workaround for "make format"

When a new enough gofumpt version is used (v0.9.0 or later), it suports the
`ignore` directive that we just added, so the workaround is no longer needed.

Co-authored-by: Stefan Haller <[email protected]>

Author: kyu08

Makefile

@@ -34,11 +34,9 @@ test: unit-test integration-test-all
 generate:
 	go generate ./...
 
-# If you execute `gofumpt -l -w .`, it will format all Go files in the current directory, including `test/_results/*` files.
-# We pass only Git-tracked Go files to gofumpt because we don't want to format the test results or get errors from it.
 .PHONY: format
 format:
-	git ls-files '*.go' ':!vendor' | xargs gofumpt -l -w
+	gofumpt -l -w .
 
 .PHONY: lint
 lint: