[SPARK-19598][SQL] Remove the alias parameter in UnresolvedRelation

## What changes were proposed in this pull request?

Remove the alias parameter in `UnresolvedRelation`, and use `SubqueryAlias` to replace it.
This can simplify some `match case` situations.

For example, the broadcast hint pull request can have one fewer case https://github.com/apache/spark/blob/master/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/analysis/ResolveHints.scala#L57-L61

## How was this patch tested?
add some unit tests

Author: windpiger <songjun@outlook.com>

Closes #16956 from windpiger/removeUnresolveTableAlias.

1 files changed, 1 insertions, 2 deletions

diff --git a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/rules.scala b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/rules.scala
index 1c3e7c6d52..e7a59d4ad4 100644
--- a/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/rules.scala
+++ b/sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/rules.scala
@@ -52,8 +52,7 @@ class ResolveSQLOnFile(sparkSession: SparkSession) extends Rule[LogicalPlan] {
           throw new AnalysisException("Unsupported data source type for direct query on files: " +
             s"${u.tableIdentifier.database.get}")
         }
-        val plan = LogicalRelation(dataSource.resolveRelation())
-        u.alias.map(a => SubqueryAlias(a, plan, None)).getOrElse(plan)
+        LogicalRelation(dataSource.resolveRelation())
       } catch {
         case _: ClassNotFoundException => u
         case e: Exception =>