Drop legacy non-container builders

iso/builder/build-in-container.sh

@@ -1,5 +1,5 @@
 #!/bin/sh
-# build-in-container.sh — build the bee ISO inside a Debian container.
+# build-in-container.sh — build the bee ISO inside the Debian builder container.
 
 set -e
 
@@ -70,6 +70,7 @@ set -- \
     run --rm --privileged \
     -v "${REPO_ROOT}:/work" \
     -v "${CACHE_DIR}:/cache" \
+    -e BEE_CONTAINER_BUILD=1 \
     -e GOCACHE=/cache/go-build \
     -e GOMODCACHE=/cache/go-mod \
     -e TMPDIR=/cache/tmp \
@@ -83,6 +84,7 @@ if [ -n "$AUTH_KEYS" ]; then
         -v "${REPO_ROOT}:/work" \
         -v "${CACHE_DIR}:/cache" \
         -v "${AUTH_KEYS_DIR}:/tmp/bee-authkeys:ro" \
+        -e BEE_CONTAINER_BUILD=1 \
         -e GOCACHE=/cache/go-build \
         -e GOMODCACHE=/cache/go-mod \
         -e TMPDIR=/cache/tmp \