Remove legacy shell tip from aggregate command

Author: milkie

source/reference/command/aggregate.txt

@@ -50,8 +50,7 @@ The command has following syntax:
    Rather than run the :dbcommand:`aggregate` command directly, most
    users should use the :method:`db.collection.aggregate()` helper
    provided in :binary:`~bin.mongosh` or the equivalent helper in
-   their driver. In 2.6 and later, the
-   :method:`db.collection.aggregate()` helper always returns a cursor.
+   their driver.
 
 Command Fields
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