[Azure] Don't mention capture_container_name in required
[Azure] Don't mention capture_container_name in required

capture_container_name is only a required variable if you are outputting
to VHD format. It is mentioned below as required when building a VHD so
having it here as well is confusing.

grubernaut/packer,timsutton/packer,dave2/packer,rnaveiras/packer,ChrisLundquist/packer,KohlsTechnology/packer,ChrisLundquist/packer,youhong316/packer,tb3088/packer,mitchellh/packer,KohlsTechnology/packer,hashicorp/packer,youhong316/packer,bryson/packer,tb3088/packer,pecigonzalo/packer,grubernaut/packer,ChrisLundquist/packer,youhong316/packer,tb3088/packer,paulmey/packer,timsutton/packer,paulmey/packer,ricardclau/packer,tas50/packer,dave2/packer,ricardclau/packer,youhong316/packer,dave2/packer,rnaveiras/packer,bryson/packer,grubernaut/packer,KohlsTechnology/packer,paulmey/packer,youhong316/packer,rnaveiras/packer,dave2/packer,ricardclau/packer,pecigonzalo/packer,dave2/packer,mitchellh/packer,ChrisLundquist/packer,timsutton/packer,pecigonzalo/packer,mitchellh/packer,bryson/packer,tas50/packer,paulmey/packer,tas50/packer,dave2/packer,mitchellh/packer,mkuzmin/packer,paulmey/packer,tb3088/packer,rnaveiras/packer,timsutton/packer,hashicorp/packer,grubernaut/packer,bryson/packer,pecigonzalo/packer,ChrisLundquist/packer,paulmey/packer,mkuzmin/packer,ricardclau/packer,KohlsTechnology/packer,KohlsTechnology/packer,mkuzmin/packer,mkuzmin/packer,hashicorp/packer,youhong316/packer,tb3088/packer,tas50/packer,mkuzmin/packer,tb3088/packer,tas50/packer,rnaveiras/packer,tas50/packer,KohlsTechnology/packer,ChrisLundquist/packer,hashicorp/packer,timsutton/packer,mkuzmin/packer,timsutton/packer,ricardclau/packer,bryson/packer,mitchellh/packer,grubernaut/packer,rnaveiras/packer,bryson/packer,ricardclau/packer,grubernaut/packer