Don't check window type in tui_set_win_focus_to

Don't check window type in tui_set_win_focus_to

This changes tui_set_win_focus_to so that it no longer checks the
window type.  Instead, now tui_unhighlight_win also checks whether the
window can be highlighted.

gdb/ChangeLog
2019-06-25  Tom Tromey  <tom@tromey.com>

	* tui/tui-win.c (tui_set_win_focus_to): Don't check window type.
	* tui/tui-wingeneral.c (tui_unhighlight_win): Check
	can_highlight.