RemoveEmpty empty.return parameter ignored during runtime

SYSTEMML-2135 Generalized the existing removeEmpty builtin function by an optional argument empty.return to control if an empty row or column is returned for empty inputs, or a matrix with zero rows or columns, respectively. By default, empty.return=TRUE to ensure backwards compatibility with SystemML 1.0.

While the Spark instruction works as expected, the related CP instruction currently ignores this parameter, leading to inconsistencies and most importantly loses backwards compatibility. Hence, this is a blocker that needs fixing for the SystemML 1.1 release.