deleted obsolete _Singular_SetRing and _Macaulay2_SetRing
prevent calling the garbage collector when a ring is in the creation phase

Some Singular rings are created in more than one call, so we prevented
the garbage collector from being invoked between the calls

(we have to alter the way the garbage collector
 gets triggered in _SetElmWPObj_ForHomalg;
 at them moment (HomalgToCAS v2013.08.07) one DeletePeriod will be omitted)