magit-show-level: don't use magit-with-refresh

We don't actually have to refresh here, since we are only changing the
`invisible' text property.
magit-stash-snapshot: don't use magit-with-refresh

We can get the same effect by only using one function that triggers a
refresh, and replacing the first call to `magit-run-git' with a call
to `magit-run-git*'.