livepatch: Remove not longer valid limitations from the documentation

Semantic changes are possible since the commit d83a7cb3
("livepatch: change to a per-task consistency model").

Also data structures can be patched since the commit 439e7271
("livepatch: introduce shadow variable API").

It is a high time we removed these limitations from the documentation.

Signed-off-by: Petr Mladek <pmladek@suse.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>