[SPARK-17250][SQL] Remove HiveClient and setCurrentDatabase from HiveSessionCatalog

### What changes were proposed in this pull request?
This is the first step to remove `HiveClient` from `HiveSessionState`. In the metastore interaction, we always use the fully qualified table name when accessing/operating a table. That means, we always specify the database. Thus, it is not necessary to use `HiveClient` to change the active database in Hive metastore.

In `HiveSessionCatalog `, `setCurrentDatabase` is the only function that uses `HiveClient`. Thus, we can remove it after removing `setCurrentDatabase`

### How was this patch tested?
The existing test cases.

Author: gatorsmile <gatorsmile@gmail.com>

Closes #14821 from gatorsmile/setCurrentDB.

sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveSessionCatalog.scala

@@ -34,7 +34,6 @@ import org.apache.spark.sql.catalyst.expressions.{Cast, Expression, ExpressionIn
 import org.apache.spark.sql.catalyst.plans.logical.{LogicalPlan, SubqueryAlias}
 import org.apache.spark.sql.catalyst.rules.Rule
 import org.apache.spark.sql.hive.HiveShim.HiveFunctionWrapper
-import org.apache.spark.sql.hive.client.HiveClient
 import org.apache.spark.sql.internal.SQLConf
 import org.apache.spark.sql.types.{DecimalType, DoubleType}
 import org.apache.spark.util.Utils
@@ -42,7 +41,6 @@ import org.apache.spark.util.Utils
 
 private[sql] class HiveSessionCatalog(
     externalCatalog: HiveExternalCatalog,
-    client: HiveClient,
     sparkSession: SparkSession,
     functionResourceLoader: FunctionResourceLoader,
     functionRegistry: FunctionRegistry,
@@ -55,11 +53,6 @@ private[sql] class HiveSessionCatalog(
     conf,
     hadoopConf) {
 
-  override def setCurrentDatabase(db: String): Unit = {
-    super.setCurrentDatabase(db)
-    client.setCurrentDatabase(db)
-  }
-
   override def lookupRelation(name: TableIdentifier, alias: Option[String]): LogicalPlan = {
     val table = formatTableName(name.table)
     if (name.database.isDefined || !tempTables.contains(table)) {

sql/hive/src/main/scala/org/apache/spark/sql/hive/HiveSessionState.scala

@@ -45,7 +45,6 @@ private[hive] class HiveSessionState(sparkSession: SparkSession)
   override lazy val catalog = {
     new HiveSessionCatalog(
       sparkSession.sharedState.externalCatalog.asInstanceOf[HiveExternalCatalog],
-      metadataHive,
       sparkSession,
       functionResourceLoader,
       functionRegistry,