Removed an unused matrix window from nmod_mat_lu_recursive, reported by krisk0.
Removed an unused matrix window from nmod_mat_lu_recursive, reported by krisk0.

fredrik-johansson/flint2,jpflori/flint2,fredrik-johansson/flint2,jpflori/flint2,dsroche/flint2,jpflori/flint2,jpflori/flint2,wbhart/flint2,dsroche/flint2,dsroche/flint2,fredrik-johansson/flint2,dsroche/flint2,wbhart/flint2,wbhart/flint2