[MINOR][SQL] Fix typo in CTAS plan database string

## What changes were proposed in this pull request?

Since [Spark 1.6.0](apache@56d7da1#diff-6f38a103058a6e233b7ad80718452387R96), there was a redundant '}' character in CTAS string plan's database argument string; `default}`. This PR aims to fix it.

**BEFORE**
```scala
scala> sc.version
res1: String = 1.6.0

scala> sql("create table t as select 1").explain
== Physical Plan ==
ExecutedCommand CreateTableAsSelect [Database:default}, TableName: t, InsertIntoHiveTable]
+- Project [1 AS _c0#3]
   +- OneRowRelation$
```

**AFTER**
```scala
scala> sql("create table t as select 1").explain
== Physical Plan ==
Execute CreateHiveTableAsSelectCommand CreateHiveTableAsSelectCommand [Database:default, TableName: t, InsertIntoHiveTable]
+- *(1) Project [1 AS 1#4]
   +- Scan OneRowRelation[]
```

## How was this patch tested?

Manual.

Closes apache#23064 from dongjoon-hyun/SPARK-FIX.

Authored-by: Dongjoon Hyun <dongjoon@apache.org>
Signed-off-by: hyukjinkwon <gurwls223@apache.org>

sql/hive/src/main/scala/org/apache/spark/sql/hive/execution/CreateHiveTableAsSelectCommand.scala

@@ -96,7 +96,7 @@ case class CreateHiveTableAsSelectCommand(
   }
 
   override def argString: String = {
-    s"[Database:${tableDesc.database}}, " +
+    s"[Database:${tableDesc.database}, " +
     s"TableName: ${tableDesc.identifier.table}, " +
     s"InsertIntoHiveTable]"
   }