[docker_test.sh] Remove useless error message

docker_test.sh

@@ -59,11 +59,6 @@ read ans
 
 if [ $ans == "y" ]; then
   git pull
-  if [[ ! -d "$1" ]]; then
-    echo "ERROR : directory does not exist ($1)"
-    usage
-    exit 1
-  fi
   cd "$1"
   git checkout -- .
 else