[SPARK-14019][SQL] Remove noop SortOrder in Sort

#### What changes were proposed in this pull request?

This PR is to add a new Optimizer rule for pruning Sort if its SortOrder is no-op. In the phase of **Optimizer**, if a specific `SortOrder` does not have any reference, it has no effect on the sorting results. If `Sort` is empty, remove the whole `Sort`.

For example, in the following SQL query
```SQL
SELECT * FROM t ORDER BY NULL + 5
```

Before the fix, the plan is like
```
== Analyzed Logical Plan ==
a: int, b: int
Sort [(cast(null as int) + 5) ASC], true
+- Project [a#92,b#93]
   +- SubqueryAlias t
      +- Project [_1#89 AS a#92,_2#90 AS b#93]
         +- LocalRelation [_1#89,_2#90], [[1,2],[1,2]]

== Optimized Logical Plan ==
Sort [null ASC], true
+- LocalRelation [a#92,b#93], [[1,2],[1,2]]

== Physical Plan ==
WholeStageCodegen
:  +- Sort [null ASC], true, 0
:     +- INPUT
+- Exchange rangepartitioning(null ASC, 5), None
   +- LocalTableScan [a#92,b#93], [[1,2],[1,2]]
```

After the fix, the plan is like
```
== Analyzed Logical Plan ==
a: int, b: int
Sort [(cast(null as int) + 5) ASC], true
+- Project [a#92,b#93]
   +- SubqueryAlias t
      +- Project [_1#89 AS a#92,_2#90 AS b#93]
         +- LocalRelation [_1#89,_2#90], [[1,2],[1,2]]

== Optimized Logical Plan ==
LocalRelation [a#92,b#93], [[1,2],[1,2]]

== Physical Plan ==
LocalTableScan [a#92,b#93], [[1,2],[1,2]]
```

cc rxin cloud-fan marmbrus Thanks!

#### How was this patch tested?
Added a test suite for covering this rule

Author: gatorsmile <gatorsmile@gmail.com>

Closes #11840 from gatorsmile/sortElimination.

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