Cleanup for sap_soap_rfc_eps_delete_file

Hi @nmonkee,

This pull requests tries to cleanup https://github.com/rapid7/metasploit-framework/pull/1659. It's applying the same changes proposed on last pull requests such as https://github.com/rapid7/metasploit-framework/pull/1658, plus is moving the module to the "dos" tree, because a file deletion module is a dos module indeed. Even when it also helps to make SMBRelay attacks, it can also be done by other auxiliary scanner modules, so I thing the auxiliary/dos/sap is the correct place for this modules. As always feel free to review, test, ask, discuss anything and merge this pull request on your repo when ready. So the original pull request will be automatically updated and we'll be ready to merge :)

Testing after changes:

```
msf auxiliary(sap_soap_rfc_eps_delete_file) > show options

Module options (auxiliary/dos/sap/sap_soap_rfc_eps_delete_file):

   Name      Current Setting  Required  Description
   ----      ---------------  --------  -----------
   CLIENT    001              yes       SAP Client
   DIRNAME   /tmp             yes       Directory Path which contains the file to delete
   FILENAME  msf.txt          yes       Filename to delete
   PASSWORD  06071992         yes       Password
   Proxies                    no        Use a proxy chain
   RHOSTS                     yes       The target address range or CIDR identifier
   RPORT     80               yes       The target port
   THREADS   1                yes       The number of concurrent threads
   USERNAME  SAP*             yes       Username
   VHOST                      no        HTTP server virtual host

msf auxiliary(sap_soap_rfc_eps_delete_file) > run

[+] 192.168.172.179:8042 - File msf.txt at /tmp successfully deleted
[*] Scanned 1 of 1 hosts (100% complete)
[*] Auxiliary module execution completed

```