[FEA] Remove support for Spark 3.1.x

[sameerz]

Is your feature request related to a problem? Please describe. Remove support for Spark 3.1, as it is more than two years old per https://spark.apache.org/news/ . It no longer receives community updates.

Describe the solution you'd like

1. Remove Spark 3.1.x shims
2. We should have removed documentation references to 3.1 support at this point. We need to scrub and reconfirm there are no mentions of Spark 3.1.x support.

Describe alternatives you've considered

Additional context