net: ipa: fix an outdated comment

Since commit 8797972a

 ("net: ipa: remove command info pool"),
we don't allocate "command info" entries for command channel
transactions.  Fix a comment that seems to suggest we still do.
(Even before that commit, the comment was out of place.)

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>