ftrace: Remove unused function ftrace_arch_read_dyn_info()

ftrace_arch_read_dyn_info() was used so that archs could add its own debug
information into the dyn_ftrace_total_info in the tracefs file system. That
file is for debugging usage of dynamic ftrace. No arch uses that function
anymore, so just get rid of it.

This also allows for tracing_read_dyn_info() to be cleaned up a bit.

Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>