CLI: dependency on kbfsfuse running

In https://github.com/termux/termux-packages/pull/2804#issuecomment-418195668 @strib mentioned that kbfsfuse shouldn't be necessary to use git-remote-keybase. However, running this resulted in an error:

```
$ keybase git create foobar123
▶ ERROR Keybase services aren't running - KBFS client not found.
```

Which was easily solved by

```
kbfsfuse -mount-type=none
```

cc @songgao

Start by reproducing `keybase git create foobar123` without running `kbfsfuse`, then compare it with the workaround `kbfsfuse -mount-type=none`. Trace the reported “KBFS client not found” check and identify the relevant CLI or service entry point. Done means git-remote-keybase works without requiring kbfsfuse, with a regression test covering the case.

Written by the indexing model from the issue text.