Remove argument optional_p from get_tracepoint_by_number

This patch is to remove parameter optional_p as it is always true,
in order to simplify get_tracepoint_by_number.

'optional_p' was added by this change,

1999-11-18  Tom Tromey  <tromey@cygnus.com>

	* tracepoint.h (get_tracepoint_by_number): Updated
	declaration.
	* tracepoint.c (trace_pass_command): Better error message.
	Fixed logic when `all' not specified.
	(get_tracepoint_by_number): Added `optional_p' argument.  Fixed
	all callers.

but after this patch,

 FYI: remove `static's from cli-utils.c
 https://sourceware.org/ml/gdb-patches/2011-03/msg00636.html

'optional_p' passed to get_tracepoint_by_number become always true.

gdb:

2014-03-06  Yao Qi  <yao@codesourcery.com>

	* breakpoint.c (get_tracepoint_by_number): Remove argument
	optional_p.  All callers updated.  Adjust comments.  Update
	output message.
	* breakpoint.h (get_tracepoint_by_number): Update declaration.