DOCSP-49961 removes legacy mongo documentation (#12323)

* DOCSP-49961 removes legacy mongo documentation

* Re-adds mongo legacy shell page

* Updates reference page

Author: jwilson-mdb

content/manual/upcoming/source/reference.txt

@@ -68,10 +68,6 @@ Manual Reference
 
 :ref:`metadata-system-collections`
    Describes the collections that MongoDB reserves for internal use.
-
-:ref:`mongo <mongo>`
-   Documentation of JavaScript methods and helpers in
-   the legacy :binary:`~bin.mongo` shell.
 
 .. seealso::
 
@@ -104,4 +100,3 @@ Manual Reference
    Slot-Based Query Execution Engine </reference/sbe>
    Stable API </reference/stable-api>
    System Collections </reference/system-collections>
-   Legacy mongo Shell </reference/mongo>

content/manual/upcoming/source/reference/mongo.txt

@@ -1,3 +1,5 @@
+:orphan:
+
 .. _mongo:
 
 .. default-domain:: mongodb