docs: staging/kprobes.rst: Update some of the references

Some of the kprobes references are not valid anymore. Update the URLs to
point to their changed locations, where appropriate. Drop two URLs which
do not exist anymore.

Reported-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Link: https://lore.kernel.org/r/ae96223716e61185870244d8f9dff6678de12fa1.1595331824.git.naveen.n.rao@linux.vnet.ibm.com


Signed-off-by: Jonathan Corbet <corbet@lwn.net>