[SPARK-19070] Clean-up dataset actions

## What changes were proposed in this pull request?
Dataset actions currently spin off a new `Dataframe` only to track query execution. This PR simplifies this code path by using the `Dataset.queryExecution` directly. This PR also merges the typed and untyped action evaluation paths.

## How was this patch tested?
Existing tests.

Author: Herman van Hovell <hvanhovell@databricks.com>

Closes #16466 from hvanhovell/SPARK-19070.