Deprecate misnamed linksys module and rename to "linux/"

As per conversation with juan and egypt in the irc channel. This linksys exploit should really be in exploit/linux, and the exploit name should describe the vuln, not the exploitation technique (no _stager). 

### Verification
- [x] Use the original module:

```
msf> use exploit/multi/http/linksys_wrt110_cmd_exec_stager
msf> exploit
```

- [x] Verify you see a big DEPRECATED warning

- [x] Verify that the you can run `check` on the new module:

```
msf> use exploit/linux/http/linksys_wrt110_cmd_exec
msf> check
[+] The target is vulnerable.
```