sh(1): Replace recommendation of use of -e with a note

This partially reverts b14cfdf665bb8b7b2898a4ee5b073ab87f8ea3d0 and has
been discussed in D42719.

Reviewed by: jrm (mentor), otis (mentor), mandree, ziaee (manpages)
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D45073