Don't track the contents of the execution info window

Don't track the contents of the execution info window

The curses library keeps track of the contents of each window, and can
redraw the screen as needed.  This means that in most cases is no need
for the TUI windows to also keep track of their contents.  This patch
removes content tracking from the execution window, leaving that to
curses.

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

	* tui/tui-winsource.h (struct tui_exec_info_window)
	<~tui_exec_info_window, maybe_allocate_content, get_content,
	m_content>: Remove.
	(struct tui_source_window_base) <set_exec_info_content,
	show_exec_info_content>: Don't declare.
	* tui/tui-winsource.c
	(tui_exec_info_window::maybe_allocate_content): Remove.
	(tui_source_window_base::update_exec_info): Rename from
	set_exec_info_content.
	(tui_source_window_base::show_exec_info_content)
	(tui_source_window_base::update_exec_info): Remove.