Uninstall dependencies before installing requirements/tpu.txt (#14586)

Signed-off-by: <ricliu@google.com>
Signed-off-by: Richard Liu <ricliu@google.com>

Dockerfile.tpu

@@ -15,6 +15,9 @@ ARG GIT_REPO_CHECK=0
 RUN --mount=type=bind,source=.git,target=.git \
     if [ "$GIT_REPO_CHECK" != 0 ]; then bash tools/check_repo.sh; fi
 
+# Remove existing versions of dependencies
+RUN pip uninstall -y torch torch_xla torchvision
+
 ENV VLLM_TARGET_DEVICE="tpu"
 RUN --mount=type=cache,target=/root/.cache/pip \
     --mount=type=bind,source=.git,target=.git \