[SQL][Minor] fix typo in comments

Removed an repeated "from" in the comments.

Author: Hongbo Liu <liuhb86@gmail.com>

Closes #4976 from liuhb86/mine and squashes the following commits:

e280e7c [Hongbo Liu] [SQL][Minor] fix typo in comments

sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala

@@ -63,7 +63,7 @@ abstract class TreeNode[BaseType <: TreeNode[BaseType]] {
 
   /**
    * Faster version of equality which short-circuits when two treeNodes are the same instance.
-   * We don't just override Object.Equals, as doing so prevents the scala compiler from from
+   * We don't just override Object.equals, as doing so prevents the scala compiler from
    * generating case class `equals` methods
    */
   def fastEquals(other: TreeNode[_]): Boolean = {