>> PS: Probably we could also add another option `no-backend'
>> that will show only an indicator and the branch name.
>> But the dangling indicator such as "-" or "*" before the branch name
>> doesn't look nice when there is a space that separates it
>> from the project name, e.g. "project -branch".
>
> It would probably make more sense to me, but having both might be overkill.
>
> FWIW, with the custom mode-line that I use (smart-mode-line) the results of
> these two options would look the same -- space-separated anyway.

Oh, this means that removing a space is useless for such mode-lines.

Ok, then let's add a much cleaner option `no-backend'.
Then anyone who doesn't like that space could customize
the mode line with something like

  (define-advice vc-mode-line (:after (&rest _args) remove-space)
    (setq vc-mode (string-trim-left vc-mode)))