kprobes: freelist.h removed

This patch will remove freelist.h from kernel source tree, since the
only use cases (kretprobe and rethook) are converted to objpool.

Link: https://lore.kernel.org/all/[email protected]/

Signed-off-by: wuqiang.matt <[email protected]>
Acked-by: Masami Hiramatsu (Google) <[email protected]>
Signed-off-by: Masami Hiramatsu (Google) <[email protected]>

Author: mattwuq