Remove indirection from tui_data_window::regs_content

Remove indirection from tui_data_window::regs_content

tui_data_window::regs_content is currently a vector of unique_ptr.
However, due to the way this is managed now, there is no need to keep
the pointers -- it can simply be a vector of the objects themselves.
This patch removes this extra layer of indirection.

2019-08-20  Tom Tromey  <tom@tromey.com>

	* tui/tui-regs.h (struct tui_data_window): Use
	DISABLE_COPY_AND_ASSIGN.
	<regs_content>: Change type, removing unique_ptr.
	<tui_data_window>: Add move constructor.
	* tui/tui-regs.c (tui_data_window::show_registers)
	(tui_data_window::show_register_group)
	(tui_data_window::display_registers_from)
	(tui_data_window::display_registers_from)
	(tui_data_window::first_data_item_displayed)
	(tui_data_window::delete_data_content_windows)
	(tui_data_window::rerender, tui_data_window::refresh_window)
	(tui_data_window::check_register_values): Update.