In the TUI, whether or not a window can be boxed is a property of the
window's type. This adds a can_box method to the window classes, and
changes tui_make_window to defer to this, removing the "box_it"
paramter. This also lets us remove "enum tui_box", as it is no longer
used.
gdb/ChangeLog
2019-08-15 Tom Tromey <tom@tromey.com>