[DataFrame][minor] cleanup unapply methods in DataTypes

Author: Wenchen Fan <cloud0fan@outlook.com>

Closes #6079 from cloud-fan/unapply and squashes the following commits:

40da442 [Wenchen Fan] one more
7d90a05 [Wenchen Fan] cleanup unapply in DataTypes

sql/catalyst/src/main/scala/org/apache/spark/sql/types/DataType.scala

@@ -47,10 +47,7 @@ abstract class DataType {
    *     ...
    * }}}
    */
-  private[sql] def unapply(a: Expression): Boolean = a match {
-    case e: Expression if e.dataType == this => true
-    case _ => false
-  }
+  private[sql] def unapply(e: Expression): Boolean = e.dataType == this
 
   /**
    * The default size of a value of this data type, used internally for size estimation.
@@ -137,10 +134,7 @@ private[sql] object IntegralType {
    *     ...
    * }}}
    */
-  def unapply(a: Expression): Boolean = a match {
-    case e: Expression if e.dataType.isInstanceOf[IntegralType] => true
-    case _ => false
-  }
+  def unapply(e: Expression): Boolean = e.dataType.isInstanceOf[IntegralType]
 }
 
 
@@ -157,10 +151,7 @@ private[sql] object FractionalType {
    *     ...
    * }}}
    */
-  def unapply(a: Expression): Boolean = a match {
-    case e: Expression if e.dataType.isInstanceOf[FractionalType] => true
-    case _ => false
-  }
+  def unapply(e: Expression): Boolean = e.dataType.isInstanceOf[FractionalType]
 }