Remove reference of GO111MODULE=off

Signed-off-by: Shengjing Zhu <zhsj@debian.org>

Vagrantfile

@@ -85,7 +85,6 @@ Vagrant.configure("2") do |config|
         curl -fsSL "https://dl.google.com/go/go${GO_VERSION}.linux-amd64.tar.gz" | tar Cxz /usr/local
         cat >> /etc/environment <<EOF
 PATH=/usr/local/go/bin:$PATH
-GO111MODULE=off
 EOF
         source /etc/environment
         cat >> /etc/profile.d/sh.local <<EOF

contrib/Dockerfile.test

@@ -35,7 +35,6 @@ RUN apt-get update && apt-get install -y \
 COPY go.mod go.mod
 COPY script/setup/install-runc install-runc
 ARG GOPROXY=direct
-ARG GO111MODULE=off
 RUN ./install-runc
 
 FROM golang-base AS dev