Remove legacy env vars from Spark diffs

[andygrove]

What is the problem the feature request solves?

The Spark diffs contain logic for the following configs:

• ENABLE_COMET_SCAN_ONLY: This is no longer set when running Spark SQL tests and should be removed from the diffs now.
• ENABLE_COMET_ANSI_MODE: This is used to enable spark.sql.ansi.enabled and does not enable any Comet features. This should be removed since there are specific tests in the Spark SQL suite for ANSI mode.

Describe the potential solution

No response

Additional context

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