Use go:generate for generating cheatsheets

This has several benefits:
- it's less code
- we're using the same mechanism to generate all our auto-generated files, so if
  someone wants to add a new one, it's clear which pattern to follow
- we can re-generate all generated files with a single command
  ("go generate ./...", or "make generate")
- we only need a single check on CI to check that all files are up to date (see
  previous commit)

Makefile

@@ -29,6 +29,7 @@ unit-test:
 .PHONY: test
 test: unit-test integration-test-all
 
+# Generate all our auto-generated files (test list, cheatsheets, maybe other things in the future)
 .PHONY: generate
 generate:
 	go generate ./...
@@ -37,10 +38,6 @@ generate:
 format:
 	gofumpt -l -w .
 
-.PHONY: update-cheatsheet
-update-cheatsheet:
-	go run scripts/cheatsheet/main.go generate
-
 # For more details about integration test, see https://github.com/jesseduffield/lazygit/blob/master/pkg/integration/README.md.
 .PHONY: integration-test-tui
 integration-test-tui: