Do not unnecessarily restrict byte update lowering of arrays

Arrays of arrays of non-constant size (as found in
regression/cbmc/Multi_Dimensional_Array6) can still be lowered by the
more general lowering code, although doing so is expensive.

Author: tautschnig

src/solvers/lowering/byte_operators.cpp

@@ -2057,11 +2057,7 @@ static exprt lower_byte_update(
       subtype = to_array_type(src.type()).subtype();
 
     auto element_width = pointer_offset_bits(*subtype, ns);
-    CHECK_RETURN(element_width.has_value());
-    CHECK_RETURN(*element_width > 0);
-    CHECK_RETURN(*element_width % 8 == 0);
-
-    if(*element_width == 8)
+    if(element_width.has_value() && *element_width == 8)
     {
       if(value_as_byte_array.id() != ID_array)
       {