Remove member count on org group (#458)

The field no longer exists in the API

Author: optik-aper

organization.go

@@ -188,7 +188,6 @@ type OrganizationGroup struct {
 	ID           string             `json:"id"`
 	Name         string             `json:"display_name"`
 	Description  string             `json:"description"`
-	MemberCount  int                `json:"member_count,omitempty"`
 	Members      []OrganizationUser `json:"members"`
 	DateCreated  string             `json:"date_created"`
 	DateAssigned string             `json:"assigned_date,omitempty"`