[pyspark] Remove the deprecated use_gpu parameter.

[trivialfis]

No description provided.

[Copilot]

Pull Request Overview

This PR removes the deprecated use_gpu parameter in favor of the device parameter across the codebase and tests.

• Consolidates GPU logic around the new device parameter in estimator and core modules
• Updates tests to replace all use_gpu usage with device="cpu" or device="cuda"
• Adjusts documentation and docstrings to drop deprecated use_gpu references

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tests/test_distributed/test_with_spark/test_spark_local.py	Replaced use_gpu in tests with device parameter
tests/test_distributed/test_gpu_with_spark/test_gpu_spark.py	Updated classifier instantiation to use device="cuda"
python-package/xgboost/spark/params.py	Changed docstring to refer to "GPU" instead of use_gpu
python-package/xgboost/spark/estimator.py	Removed deprecated use_gpu import, warning, and handling
python-package/xgboost/spark/core.py	Removed use_gpu param and default; updated _run_on_gpu logic

[trivialfis]

@wbo4958

[wbo4958]

LGTM. But better to involve @WeichenXu123 to be aware of this PR.