remove unnecessary circle.yml

circle.yml

@@ -1,13 +1,6 @@
 machine:
   timezone:
     Asia/Tokyo
-  environment:
-    GODIST: "go1.8.1.linux-amd64.tar.gz"
-  post:
-    - mkdir -p download
-    - test -e download/$GODIST || curl -o download/$GODIST https://storage.googleapis.com/golang/$GODIST
-    - sudo rm -rf /usr/local/go
-    - sudo tar -C /usr/local -xzf download/$GODIST
 test:
   override:
     - GOOS=linux GOARCH=amd64 go test -v ./...