Update docker compose files (#11380)

Version is no longer needed, ref readthedocs/common#215.

Author: stsewd

docker-compose.override.yml

@@ -10,8 +10,6 @@
 # instead we need to hit NGINX's IP (this is used on Embed API from
 # -ext for example) Setting a static IP for NGINX, allow us to
 # override /etc/hosts with this IP.
-version: '3'
-
 networks:
   readthedocs:
     driver: bridge

dockerfiles/docker-compose-assets.yml

@@ -1,5 +1,3 @@
-version: '3'
-
 services:
   assets:
     image: node:8.16