Switch to calling api

Test cover in
CRM_Member_BAO_MembershipTest::testMembershipUpdateDoesNotDeleteRelatedMembershipsByMistake

CRM/Contact/BAO/Relationship.php

@@ -2431,7 +2431,7 @@ SELECT count(*)
     AND is_current_member = 1";
     $result = CRM_Core_DAO::singleValueQuery($query);
     if ($result < CRM_Utils_Array::value('max_related', $membershipValues, PHP_INT_MAX)) {
-      CRM_Member_BAO_Membership::create($membershipValues);
+      civicrm_api3('Membership', 'create', $membershipValues);
     }
     return $membershipValues;
   }