tracing: Move tracing_set_filter_buffering() into trace_events_hist.c

tracing: Move tracing_set_filter_buffering() into trace_events_hist.c

The function tracing_set_filter_buffering() is only used in
trace_events_hist.c. Move it to that file and make it static.

Cc: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Link: https://patch.msgid.link/20260206195936.617080218@kernel.org
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>