Revert "buildGoModule: set GOPROXY to go default"

      runHook preConfigure

      export GOCACHE=$TMPDIR/go-cache

      export GOPATH="$TMPDIR/go"

      # fixes 'GOPROXY list is not the empty string, but contains no entries'

      # "https://proxy.golang.org,direct" is the go default

      export GOPROXY="''${GOPROXY:-"https://proxy.golang.org,direct"}" # respect impureEnvVars

      cd "${modRoot}"

      runHook postConfigure

    '';