scripts/updatedep: remove "dep prune" command

"Pruning is now performed automatically by dep ensure."

Signed-off-by: Gyuho Lee <gyuhox@gmail.com>

scripts/updatedep.sh

@@ -16,5 +16,3 @@ else
   # shellcheck disable=SC2086
   dep ensure -v -update $1
 fi
-
-dep prune