Currently, stream_session::prepare throws when a table in requests
or summaries is dropped. However, we do not want to fail streaming
if the table is dropped.
Delete table checks from stream_session::prepare. Further streaming
steps can handle the dropped table and finish the streaming successfully.
Fixes: #15257.
Closesscylladb/scylladb#23915
(cherry picked from commit 20c2d6210e)
Closesscylladb/scylladb#24053