Simplify tui_make_all_invisible

Simplify tui_make_all_invisible

This simplifies the implementation of tui_make_all_invisible.  Also,
because show_data is only called by show_layout, this hoists the call
to tui_make_all_invisible and removes the call from show_data.

gdb/ChangeLog
2019-08-13  Tom Tromey  <tom@tromey.com>

	* tui/tui-wingeneral.c (make_all_visible): Remove.
	(tui_make_all_invisible): Simplify.
	* tui/tui-layout.c (tui_make_all_invisible): Move from
	tui-wingeneral.c; simplify.
	(show_layout): Hoist call to tui_make_all_invisible.
	(show_data): Don't call tui_make_all_invisible.