dix: Don't send touch end to clients that do async grab without touches

GTK3 menu widget creates a selection for touch and other events and
after receiving touch events creates an async grab that excludes touch
events. Unfortunately it relies on X server not sending the touch end
event in order to function properly. Sending touch end event will cause
it to think that the initiating touch ended and when it actually ends,
the ButtonRelease event will make it think that the menu should be
closed. As a result, the menu will be open only for the duration of the
touch making it useless.

This commit reverts f682e056.

Fixes: xorg/xserver#1255

Signed-off-by: Povilas Kanapickas <povilas@radix.lt>
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