trace_syscalls: Remove unused syscall_name_to_nr()

After duplications are removed, syscall_name_to_nr() is unused.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Acked-by: Jason Baron <jbaron@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <4B14D2A6.6060803@cn.fujitsu.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>