gh-154788: Make curses window.getparent() unconditional (GH-154789)

gh-154788: Make curses window.getparent() unconditional (GH-154789)

getparent() calls no curses function, it returns the window's stored parent,
but it was compiled only when the ncurses extension functions were present.
Close the guard after getscrreg(), which does need it.

The test moves out of test_state_getters, which is gated on is_scrollok(), so
that getparent() is covered on backends without the extensions.