man: replace tablet shell with kiosk shell

Tablet shell was removed in 873b515aee in
2013. Time to remove the hopefully last reference to it.

We also gained kiosk shell in the mean time, so mention that instead.
Yes, it's a bit of a lie, because we also have ivi-shell and
fullscreen-shell, but I heard they might be on their way out, so I
didn't add them here.

Would be nice to add kiosk-shell in the SHELLS section too, but in this
patch I am only concerned about dropping the tablet shell reference.

Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>

man/weston.man

@@ -14,7 +14,7 @@ modesetting via DRM), as an X client, or inside another Wayland server
 instance.
 
 Weston supports fundamentally different graphical user interface paradigms via
-shell plugins. Two plugins are provided: the desktop shell, and the tablet
+shell plugins. Two plugins are provided: the desktop shell, and the kiosk
 shell.
 
 Weston also supports X clients via