[REF] Change function signature to support moving this off the form layer

[REF] Change function signature to support moving this off the form layer

This is really a business logic function & belongs on the BAO. This change simply removes the
access to  such that it can be moved by making it an input parameter.

Next step would be o make it static & move  it to CRM_Member_BAO_Membership

Evenually this should not be called by the form as the CRM_Member_BAO_Membership
::create function will call it