tracing: Remove duplicate struct declaration in trace_events.h

struct trace_array is declared twice. One has been declared
at forward declaration. Remove the duplicate.

Link: https://lkml.kernel.org/r/20210330034056.2266969-1-wanjiabing@vivo.com



Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>