[SPARK-16476] Restructure MimaExcludes for easier union excludes
[SPARK-16476] Restructure MimaExcludes for easier union excludes

## What changes were proposed in this pull request?
It is currently fairly difficult to have proper mima excludes when we cut a version branch. I'm proposing a small change to take the exclude list out of the exclude function, and put it in a variable so we can easily union excludes.

After this change, we can bump pom.xml version to 2.1.0-SNAPSHOT, without bumping the diff base version. Note that I also deleted all the exclude rules for version 1.x, to cut down the size of the file.

## How was this patch tested?
N/A - this is a build infra change.

Author: Reynold Xin <c9d35a384bc579d1c6c8c055f2a2b5c04e11b521@databricks.com>

Closes #14128 from rxin/SPARK-16476.

(cherry picked from commit 52b5bb0b7fabe6cc949f514c548f9fbc6a4fa181)
Signed-off-by: Reynold Xin <c9d35a384bc579d1c6c8c055f2a2b5c04e11b521@databricks.com>

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