Fix local go_lintfix errors (#5191)

* lint: add make lintfix and run it

Fixes all errors like:
```
File is not `goimports`-ed with -local github.com/tilt-dev/tilt (goimports)
```

* git: change to use TrimSuffix

* build: remove unnecessary cast

pkg/watch/watcher_nonwin.go

@@ -1,3 +1,4 @@
+//go:build !windows
 // +build !windows
 
 package watch