## What changes were proposed in this pull request?

Documentation changes to indicate that fine-grained mode is now deprecated.  No code changes were made, and all fine-grained mode instructions were left in place.  We can remove all of that once the deprecation cycle completes (Does Spark have a standard deprecation cycle?  One major version?)

Blocked on https://github.com/apache/spark/pull/14059

## How was this patch tested?

Viewed in Github

Author: Michael Gummelt <mgummelt@mesosphere.io>

Closes #14078 from mgummelt/deprecate-fine-grained.