Docs: Remove serverless

For now Scylla Cloud Serverless does not exist, so there is no point in
keeping its docs. If it is ever brought back, we can restore the docs
from git.

Author: Lorak-mmk

docs/index.rst

@@ -53,9 +53,6 @@ Contents
 :doc:`scylla-cloud`
     Connect to ScyllaDB Cloud
 
-:doc:`scylla-cloud-serverless`
-    Connect to ScyllaDB Cloud Serverless
-
 :doc:`faq`
     A collection of Frequently Asked Questions
 
@@ -79,7 +76,6 @@ Contents
    object-mapper
    dates-and-times
    scylla-cloud
-   scylla-cloud-serverless
    faq
 
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