Remove has_locator method

Remove has_locator method

Earlier changes made it obvious that the has_locator method can only
be called for source/disassembly windows.  Because the only reference
to this now occurs in methods on this object, we can remove the
has_locator method entirely, in favor of using the member directly.

gdb/ChangeLog
2019-07-17  Tom Tromey  <tom@tromey.com>

	* tui/tui-win.c (tui_source_window_base::set_new_height)
	(tui_source_window_base::do_make_visible_with_new_height): Use
	m_has_locator field directly.
	* tui/tui-data.h (struct tui_win_info) <has_locator>: Remove
	method.
	(struct tui_source_window_base) <has_locator>: Likewise.