Use Colab CPU base image. (#1534)

* Remove the config.txt file. We only set the BASE_IMAGE now, move that
to the Dockerfile.tmpl for simplicity.

http://b/479244898

Author: rosbo

Dockerfile.tmpl

@@ -1,7 +1,8 @@
-ARG BASE_IMAGE \
-    BASE_IMAGE_TAG
-
-FROM ${BASE_IMAGE}:${BASE_IMAGE_TAG}
+{{ if eq .Accelerator "gpu" }}
+FROM us-docker.pkg.dev/colab-images/public/runtime:release-colab-external_20260126-060048_RC00
+{{ else }}
+FROM us-docker.pkg.dev/colab-images/public/cpu-runtime:release-colab-external_20260123-060023_RC00
+{{ end}}
 
 ADD kaggle_requirements.txt /kaggle_requirements.txt
 

build

@@ -47,18 +47,13 @@ done
 BUILD_ARGS+=" --build-arg GIT_COMMIT=$(git rev-parse HEAD)"
 BUILD_ARGS+=" --build-arg BUILD_DATE=$(date '+%Y%m%d-%H%M%S')"
 
-# Read build args from config.txt file.
-SRCDIR=$(dirname "${BASH_SOURCE[0]}")
-for l in `cat ${SRCDIR}/config.txt`; do
-    BUILD_ARGS+=" --build-arg $l"
-done
-
 readonly CACHE_FLAG
 readonly DOCKERFILE
 readonly ACCELERATOR
 readonly IMAGE_TAG
 readonly BUILD_ARGS
 
+SRCDIR=$(dirname "${BASH_SOURCE[0]}")
 DOCKERFILE_OUTDIR="${SRCDIR}/.generated"
 mkdir -p $DOCKERFILE_OUTDIR
 DOCKERFILE_PATH="$DOCKERFILE_OUTDIR/$DOCKERFILE"