[SPARK-19148][SQL][FOLLOW-UP] do not expose the external table concept in Catalog

### What changes were proposed in this pull request?
After we renames `Catalog`.`createExternalTable` to `createTable` in the PR: apache#16528, we also need to deprecate the corresponding functions in `SQLContext`.

### How was this patch tested?
N/A

Author: Xiao Li <[email protected]>

Closes apache#17502 from gatorsmile/deprecateCreateExternalTable.

Author: gatorsmile

sql/core/src/main/scala/org/apache/spark/sql/SQLContext.scala

@@ -17,7 +17,6 @@
 
 package org.apache.spark.sql
 
-import java.beans.BeanInfo
 import java.util.Properties
 
 import scala.collection.immutable
@@ -527,8 +526,9 @@ class SQLContext private[sql](val sparkSession: SparkSession)
    * @group ddl_ops
    * @since 1.3.0
    */
+  @deprecated("use sparkSession.catalog.createTable instead.", "2.2.0")
   def createExternalTable(tableName: String, path: String): DataFrame = {
-    sparkSession.catalog.createExternalTable(tableName, path)
+    sparkSession.catalog.createTable(tableName, path)
   }
 
   /**
@@ -538,11 +538,12 @@ class SQLContext private[sql](val sparkSession: SparkSession)
    * @group ddl_ops
    * @since 1.3.0
    */
+  @deprecated("use sparkSession.catalog.createTable instead.", "2.2.0")
   def createExternalTable(
       tableName: String,
       path: String,
       source: String): DataFrame = {
-    sparkSession.catalog.createExternalTable(tableName, path, source)
+    sparkSession.catalog.createTable(tableName, path, source)
   }
 
   /**
@@ -552,11 +553,12 @@ class SQLContext private[sql](val sparkSession: SparkSession)
    * @group ddl_ops
    * @since 1.3.0
    */
+  @deprecated("use sparkSession.catalog.createTable instead.", "2.2.0")
   def createExternalTable(
       tableName: String,
       source: String,
       options: java.util.Map[String, String]): DataFrame = {
-    sparkSession.catalog.createExternalTable(tableName, source, options)
+    sparkSession.catalog.createTable(tableName, source, options)
   }
 
   /**
@@ -567,11 +569,12 @@ class SQLContext private[sql](val sparkSession: SparkSession)
    * @group ddl_ops
    * @since 1.3.0
    */
+  @deprecated("use sparkSession.catalog.createTable instead.", "2.2.0")
   def createExternalTable(
       tableName: String,
       source: String,
       options: Map[String, String]): DataFrame = {
-    sparkSession.catalog.createExternalTable(tableName, source, options)
+    sparkSession.catalog.createTable(tableName, source, options)
   }
 
   /**
@@ -581,12 +584,13 @@ class SQLContext private[sql](val sparkSession: SparkSession)
    * @group ddl_ops
    * @since 1.3.0
    */
+  @deprecated("use sparkSession.catalog.createTable instead.", "2.2.0")
   def createExternalTable(
       tableName: String,
       source: String,
       schema: StructType,
       options: java.util.Map[String, String]): DataFrame = {
-    sparkSession.catalog.createExternalTable(tableName, source, schema, options)
+    sparkSession.catalog.createTable(tableName, source, schema, options)
   }
 
   /**
@@ -597,12 +601,13 @@ class SQLContext private[sql](val sparkSession: SparkSession)
    * @group ddl_ops
    * @since 1.3.0
    */
+  @deprecated("use sparkSession.catalog.createTable instead.", "2.2.0")
   def createExternalTable(
       tableName: String,
       source: String,
       schema: StructType,
       options: Map[String, String]): DataFrame = {
-    sparkSession.catalog.createExternalTable(tableName, source, schema, options)
+    sparkSession.catalog.createTable(tableName, source, schema, options)
   }
 
   /**
@@ -1089,9 +1094,9 @@ object SQLContext {
    * method for internal use.
    */
   private[sql] def beansToRows(
-        data: Iterator[_],
-        beanClass: Class[_],
-        attrs: Seq[AttributeReference]): Iterator[InternalRow] = {
+      data: Iterator[_],
+      beanClass: Class[_],
+      attrs: Seq[AttributeReference]): Iterator[InternalRow] = {
     val extractors =
       JavaTypeInference.getJavaBeanReadableProperties(beanClass).map(_.getReadMethod)
     val methodsToConverts = extractors.zip(attrs).map { case (e, attr) =>