Remove duplicate sentence from alarm() doc.

 (backport from rev. 56143)

Doc/lib/libsignal.tex

@@ -101,8 +101,7 @@ The \module{signal} module defines the following functions:
   be scheduled at any time).  The returned value is then the number of
   seconds before any previously set alarm was to have been delivered.
   If \var{time} is zero, no alarm is scheduled, and any scheduled
-  alarm is canceled.  The return value is the number of seconds
-  remaining before a previously scheduled alarm.  If the return value
+  alarm is canceled.  If the return value
   is zero, no alarm is currently scheduled.  (See the \UNIX{} man page
   \manpage{alarm}{2}.)
   Availability: \UNIX.