Remove lint.sh; re-add 'make fmt' (#2113)

See Makefile for explanation on difference between 'make fmt' and 'make
lint'.

I also removed lint.sh. Original motivation was to use it in aider, but
it's not a good fit there, because aider passes filenames and it does
not work well with most golang linters which requires whole packages to
work.

Follow up to #2062, #2056, #2051.

Makefile

@@ -5,11 +5,17 @@ PACKAGES=./acceptance/... ./libs/... ./internal/... ./cmd/... ./bundle/... .
 GOTESTSUM_FORMAT ?= pkgname-and-test-fails
 
 lint:
-	./lint.sh ./...
+	golangci-lint run --fix
 
 lintcheck:
 	golangci-lint run ./...
 
+# Note 'make lint' will do formatting as well. However, if there are compilation errors,
+# formatting/goimports will not be applied by 'make lint'. However, it will be applied by 'make fmt'.
+# If you need to ensure that formatting & imports are always fixed, do "make fmt lint"
+fmt:
+	golangci-lint run --enable-only="gofmt,gofumpt,goimports" --fix ./...
+
 test:
 	gotestsum --format ${GOTESTSUM_FORMAT} --no-summary=skipped -- ${PACKAGES}
 
@@ -39,4 +45,4 @@ integration:
 integration-short:
 	$(INTEGRATION) -short
 
-.PHONY: lint lintcheck test cover showcover build snapshot vendor schema integration integration-short
+.PHONY: lint lintcheck fmt test cover showcover build snapshot vendor schema integration integration-short