[SPARK-22159][SQL] Make config names consistently end with "enabled".

## What changes were proposed in this pull request?
spark.sql.execution.arrow.enable and spark.sql.codegen.aggregate.map.twolevel.enable -> enabled

## How was this patch tested?
N/A

Author: Reynold Xin <rxin@databricks.com>

Closes #19384 from rxin/SPARK-22159.