Remove curl after the usage (#6347)

Dockerfile

@@ -14,7 +14,7 @@ WORKDIR /go/src/github.com/minio/
 COPY dockerscripts/docker-entrypoint.sh dockerscripts/healthcheck.sh /usr/bin/
 
 RUN  \
-     apk add --no-cache ca-certificates curl && \
+     apk add --no-cache ca-certificates && \
      apk add --no-cache --virtual .build-deps git && \
      echo 'hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4' >> /etc/nsswitch.conf && \
      go get -v -d github.com/minio/minio && \

Dockerfile.dev

@@ -16,7 +16,7 @@ COPY dockerscripts/docker-entrypoint.sh dockerscripts/healthcheck.sh /usr/bin/
 COPY . /go/src/github.com/minio/minio
 
 RUN  \
-     apk add --no-cache ca-certificates curl && \
+     apk add --no-cache ca-certificates && \
      apk add --no-cache --virtual .build-deps git && \
      echo 'hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4' >> /etc/nsswitch.conf && \
      cd /go/src/github.com/minio/minio && \

Dockerfile.release

@@ -13,6 +13,7 @@ RUN \
      apk add --no-cache --virtual .build-deps curl && \
      echo 'hosts: files mdns4_minimal [NOTFOUND=return] dns mdns4' >> /etc/nsswitch.conf && \
      curl https://dl.minio.io/server/minio/release/linux-amd64/minio > /usr/bin/minio && \
+     apk del .build-deps && \
      chmod +x /usr/bin/minio  && \
      chmod +x /usr/bin/docker-entrypoint.sh && \
      chmod +x /usr/bin/healthcheck.sh