maintainer-pgp-guide: minor wording tweaks

Tweak some wording to remove redundant information.

Signed-off-by: Konstantin Ryabitsev <konstantin@linuxfoundation.org>
Link: https://lore.kernel.org/r/20220727-docs-pgp-guide-v2-5-e3e6954affb6@linuxfoundation.org


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