In `repo.RemoveDependency`, use `PostFormValue` instead of
`PostForm.Get`. The latter requires `ParseForm()` to be called prior,
and in this case, has no benefit over `PostFormValue` anyway (which
calls `ParseForm()` if necessary).
While this currently does not cause any issue as far as I can tell, it
feels like a bug lying in wait for the perfect opportunity. Lets squash
it before it can do harm.
Signed-off-by: Gergely Nagy <forgejo@gergo.csillger.hu>