Remove quotation marks around effective caller name

Quotation marks around effective caller name don't work with phone number (double quoted in SIP header), so that this command:
```EXECUTE sofia/external/089123112312@sipconnect.sipgate.de set(effective_caller_id_name='498910002000')```
leads to this SIP header:
```From: "'498910002000'" <sip:```
which for obvious reasons is not accepted by the SIP trunk.