build: Don't automatically pull images when building

Automatically pulling is good for getting an up-to-date base image, but
it's too easy to trip docker hub's rate limiting and get blocked, which
then prevents the builds from proceeding.

Author: mpe

build/scripts/image.sh

@@ -86,10 +86,6 @@ fi
 
 cmd="$DOCKER build -f $distro/Dockerfile "
 
-if [[ "$distro" != "ubuntu-allcross" ]]; then
-    cmd+="--pull "
-fi
-
 if [[ -n "$http_proxy" ]]; then
     cmd+="--build-arg http_proxy=$http_proxy "
 fi