nfs-utils: remove possibly false statement from exports.man

A very minor change suggested by J. Bruce Fields <bfields@fieldses.org>
to remove the statement that exporting to a single host or IP address is
the "most common format" - as it probably isn't.

Signed-off-by: James Pearson <james-p@moving-picture.com>
Signed-off-by: Steve Dickson <steved@redhat.com>