matobj: revert some Semigroups-related downrankings

Three downrankings were added in advance of GAP 4.10, to make
sure that GAP did not break the Semigroups package, but only
one of them was actually required. This commit reverts the
other two.

lib/matobj.gi

@@ -184,9 +184,6 @@ InstallMethod( Matrix,
 #
 InstallMethod( Matrix,
   [IsSemiring, IsList, IsInt],
-  # FIXME: Remove this downranking, it was introduced to prevent
-  #        Semigroups from breaking ahead of the 4.10 release
-  -SUM_FLAGS,
   function( basedomain, list, nrCols )
     local rep;
     rep := DefaultMatrixRepForBaseDomain(basedomain);
@@ -195,9 +192,6 @@ InstallMethod( Matrix,
 
 InstallMethod( Matrix,
   [IsSemiring, IsList],
-  # FIXME: Remove this downranking, it was introduced to prevent
-  #        Semigroups from breaking ahead of the 4.10 release
-  -SUM_FLAGS,
   function( basedomain, list )
     local rep;
     if Length(list) = 0 then Error("list must be not empty"); fi;