Implement remove of uri

### Environment
* Phabfive version: 0.1.0
* Python version: 3.6

### Proposed Functionality

Current functionality

```
$ phabfive diffusion
Usage:
phabfive diffusion repo list [(active || inactive || all)] [options]
phabfive diffusion repo create [options]
phabfive diffusion uri create (--observe || --mirror) () [options]
phabfive diffusion uri list [options]
phabfive diffusion branch list [options]
```

Implement following behaviour

```
$ phabfive diffusion uri remove REPO https://foo/bar.git
Removed https://foo/bar.git from REPO

$ echo $?
0

$ phabfive diffusion uri remove REPO https://foo/non-existant.git
Unable to remove non-existant https://foo/non-existant.git from REPO

$ echo $?
0
```

### Use Case

Enable ues to remove URI from phabricator