[exec.snd.general] Remove disconnected and obsolete paragraph.

Author: tkoeppe

source/exec.tex

@@ -1222,11 +1222,6 @@
 
 \rSec2[exec.snd.general]{General}
 
-\pnum
-For the purposes of this subclause,
-a sender is an object
-whose type satisfies the sender concept\iref{exec.async.ops}.
-
 \pnum
 Subclauses \ref{exec.factories} and \ref{exec.adapt} define
 customizable algorithms that return senders.