make default discard and mute_ring hooks forward to missed_call using sxmo_hooks.sh

Signed-off-by: Stacy Harper <contact@stacyharper.net>

configs/default_hooks/discard

@@ -2,4 +2,5 @@
 
 # This script is executed (asynchronously) when you discard an incoming call
 
-exec "$(dirname "$0")/missed_call" "$@"
+# just do the same as the missed_call hook:
+exec sxmo_hooks.sh missed_call "$@"

configs/default_hooks/mute_ring

@@ -2,4 +2,5 @@
 
 # This script is executed (asynchronously) when you mute an incoming call
 
-exec "$(dirname "$0")/missed_call" "$@"
+# just do the same as the missed_call hook:
+exec sxmo_hooks.sh missed_call "$@"