Remove tui_clear_win_detail

Remove tui_clear_win_detail

An earlier patch changed the context of the sole call to
tui_clear_win_detail to make it clear that this can never be called
with a NULL window pointer.  So, remove tui_clear_win_detail in favor
of calling the method directly.

gdb/ChangeLog
2019-06-25  Tom Tromey  <tom@tromey.com>

	* tui/tui-data.h (tui_clear_win_detail): Don't declare.
	* tui/tui-data.c (tui_clear_source_windows_detail): Call the
	clear_detail method directly.
	(tui_clear_win_detail): Remove.