Remove attr from ListResource.
Remove attr from ListResource.

Not sure what the effect is, but more tests are passing. May need to add some
more tests around Phone number behavior.

achoe/twilio-php,javierwilson/twilio-php,sayan801/twilio-php,pablophg/twilio-php,beachboysapp/urgentMe,beachboysapp/urgentMe,FTrubitz/twilio-php,MartinAmps/twilio-php,Git-Host/twilio-php,twilio/twilio-php