Documentation/kdump: Remove TODO in this document

We have already had the relocatable kernel, so just remove
the TODO in the kdump document.

Signed-off-by: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Acked-by: Rob Landley <rob@landley.net>
Acked-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>