Remove unused variable

Fixes compiler warning on unused variable which was left over in the
9.3 merge.
Reviewed-by: NHeikki Linnakangas <hlinnakangas@pivotal.io>

src/backend/tcop/idle_resource_cleaner.c

@@ -22,7 +22,6 @@
 int			IdleSessionGangTimeout = 18000;
 
 static volatile sig_atomic_t clientWaitTimeoutInterruptEnabled = 0;
-static volatile sig_atomic_t clientWaitTimeoutInterruptOccurred = 0;
 
 static volatile sig_atomic_t idle_gang_timeout_occurred;