Remove tui_show_disassem

Remove tui_show_disassem

tui_show_disassem is just a wrapper for the update_source_window
method, and it only has a single caller.  This removes the function
and inlines the logic into that caller.

gdb/ChangeLog
2019-12-20  Tom Tromey  <tom@tromey.com>

	* tui/tui-winsource.c (tui_update_source_windows_with_addr): Call
	update_source_window directly.
	* tui/tui-disasm.h (tui_show_disassem): Don't declare.
	* tui/tui-disasm.c (tui_show_disassem): Remove.

Change-Id: I7ae7a3309f64a4a949c07a80c46e1664c7f12913