This PR removes the usage of the custom `mongodb_proxy` package from
edx-platform, replacing it with MongoDB's built-in retry functionality via
`retryReads=True`.
Changes:
* Removed all references to `mongodb_proxy.MongoProxy` from connection logic.
* Updated `connect_to_mongodb()` to always use `retryReads=True`.
* Uninstalled `openedx-mongodbproxy` from edx-platform requirements.
Fixes: https://github.com/openedx/edx-platform/issues/35210