remove bogus \/ escapes

some X manuals use then escape sequence \/ when they want to render
a slash.  That's bad because \/ is not a slash but an italic
correction, never producing any output, having no effect at all in
terminal output, and only changing spacing in a minor way in typeset
output.

Signed-off-by: Matthieu Herrb <matthieu@herrb.eu>
Reviewed-by: Mark Kettenis <kettenis@openbsd.org>
Signed-off-by: Keith Packard <keithp@keithp.com>