Fix minor quoting problems in doc strings

Fix minor quoting problems in doc strings

These were glitches regardless of how or whether we tackle the
problem of grave accent in doc strings.

* gnus-art.el (gnus-treat-strip-list-identifiers)
(gnus-article-mode-syntax-table):
* gnus-group.el (gnus-group-nnimap-edit-acl):
* canlock.el, deuglify.el: Fix minor quoting problems in doc strings,
e.g., missing quote, ``x'' where `x' was meant, etc.