DOCS-12853: [Atlas] Documentation still suggests atlas migrate only works with replica sets (#128)

* DOCS-12853: [Atlas] Documentation still suggests atlas migrate only works with replica sets

Author: steveren

source/includes/steps-import.yaml

@@ -4,7 +4,6 @@ level: 4
 stepnum: 1
 content: |
 
-
   You will be using a product inventory database for the ``CRUD Getting
   Started`` guides. Download the `inventory.crud.json file
   <https://raw.githubusercontent.com/mongodb/docs-assets/primer-

source/includes/steps-migration_pr.yaml

@@ -10,7 +10,7 @@ content: |
    for help with your migration.
 
 ---
-title: Your current MongoDB database is running MongoDB 2.6+
+title: Your current MongoDB database is running MongoDB 2.6 or higher.
 ref: mongodb-version
 level: 4
 stepnum: 2
@@ -26,32 +26,15 @@ content: |
    for upgrade instructions.
 
 ---
-title: Your current deployment is a MongoDB replica set.
+title: Your current deployment is a MongoDB replica set or sharded cluster.
 ref: mongod-replica-set
 level: 4
 stepnum: 3
 content: |
 
    If your deployment is currently a standalone instance, you must first
    :manual:`convert it to a replica set </tutorial/convert-standalone-to-replica-set>`.
-   Live migration of data from sharded clusters is not supported. 
----
-title: Authentication is enabled on your source deployment
-ref: authentication-enabled
-level: 4
-stepnum: 4
-content: |
-
-   The migration process requires that authentication is enabled on your
-   source cluster in AWS. See :manual:`Enable Auth </tutorial/enable-authentication>`
-   for instructions on enabling authentication.
-
-   You can verify that authentication is enabled on your source cluster
-   using the :manual:`mongo </reference/program/mongo/>` command:
-
-   .. code-block:: sh 
 
-      mongo <mongodb-connection-string> -u <mongodb-username> -p --authenticationDatabase admin
 ---
 title: The database user from your source cluster on AWS that you will use
        to perform the migration has the required MongoDB roles.