ftrace: Remove freeing of old_hash from ftrace_hash_move()

ftrace_hash_move() currently frees the old hash that is passed to it
after replacing the pointer with the new hash. Instead of having the
function do that chore, have the caller perform the free.

This lets the ftrace_hash_move() be used a bit more freely, which
is needed for changing the way the trampoline logic is done.

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