chore: remove unnecessary env (#1654)

tools/goctl/docker/template.go

@@ -13,7 +13,6 @@ const (
 LABEL stage=gobuilder
 
 ENV CGO_ENABLED 0
-ENV GOOS linux
 {{if .Chinese}}ENV GOPROXY https://goproxy.cn,direct
 {{end}}{{if .HasTimezone}}
 RUN apk update --no-cache && apk add --no-cache tzdata