replace notmuch::reviewed with an equivalent query

nmbug commit 433ff6b859781288daa2c762d6d8427d8b332f79 removes that tag
from all messages.

notmuch::reviewed is useless and is not used since 2011 (except once).
It wasn't mentioned in wiki (except for one example) and
http://nmbug.tethera.net/status/ . There were only 8 threads with this
tag.