Do not include Docker version in caching key

We are now using Docker caching directly rather than downloading archives from S3, so it should not be needed.

This should unblock reusing the cache locally.

Author: Kobzol

src/ci/docker/run.sh

@@ -71,8 +71,6 @@ if [ -f "$docker_dir/$image/Dockerfile" ]; then
       # only run in x86_64 machines.
       uname -m >> $hash_key
 
-      docker --version >> $hash_key
-
       # Include cache version. Can be used to manually bust the Docker cache.
       echo "2" >> $hash_key