Revert "Keras 3 w/ tf2.16 (#1385)"

This reverts commit e3181fe.

tpu/Dockerfile

@@ -65,10 +65,14 @@ RUN pip install tensorflow_hub https://storage.googleapis.com/cloud-tpu-tpuvm-ar
     papermill jupyterlab python-lsp-server[all] "jupyter-lsp==1.5.1" \
     pandas matplotlib opencv-python-headless librosa accelerate diffusers scikit-learn transformers \
     seaborn timm albumentations einops pyarrow fastparquet opencv-python \
-    "keras>3" keras-cv keras-nlp \
     kagglehub && \
     /tmp/clean-layer.sh
 
+# b/318672157 Install Keras 3 for loading models.
+# We ignore dependencies for now since tf2.15 should work despite pip saying it won't.
+RUN pip install --no-dependencies "keras>3" keras-cv keras-nlp && \
+    /tmp/clean-layer.sh
+
 # Tensorflow libtpu:
 RUN curl --output /lib/libtpu.so https://storage.googleapis.com/cloud-tpu-tpuvm-artifacts/libtpu/${TF_LIBTPU_VERSION}/libtpu.so