Remove some calls in tui_data_window

Remove some calls in tui_data_window

This patch removes a call to erase_data_content in refresh_all and
then removes some other calls that are more clearly unnecessary once
one follows calls from that point.

gdb/ChangeLog
2019-08-30  Tom Tromey  <tom@tromey.com>

	* tui/tui-regs.c (tui_data_window::display_registers_from_line)
	(tui_data_window::rerender): Don't call
	check_and_display_highlight_if_needed.
	(tui_data_window::refresh_all): Remove call to
	erase_data_content.