doc: hide the redundant ToC on the Alternator page

This commit hides the ToC, as we don't need it, especially at the end of the page.
The ToC must be hidden rather than removed because removing it would, in turn,
remove the "Getting Started With ScyllaDB Alternator" and "ScyllaDB Alternator for DynamoDB users"
from the page tree and make them inaccessible.

docs/alternator/alternator.md

@@ -208,6 +208,7 @@ with Tablets enabled.
 ```{eval-rst}
 .. toctree::
     :maxdepth: 2
+    :hidden:
 
     getting-started
     compatibility