arm64: Drop outdated links in comments

arm64: Drop outdated links in comments

As started by commit 05a5f51ca566 ("Documentation: Replace lkml.org links
with lore"), an effort was made to replace lkml.org links with lore to
better use a single source that's more likely to stay available long-term.
However, it seems these links don't offer much value here, so just
remove them entirely.

Cc: Joe Perches <joe@perches.com>
Suggested-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/lkml/20210211100213.GA29813@willie-the-truck/
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20211215191835.1420010-1-keescook@chromium.org
[catalin.marinas@arm.com: removed the arch/arm changes]
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>