SOLR-17851: Remove BlobHandler and .system collection support

[epugh]

https://issues.apache.org/jira/browse/SOLR-17851

Description

Remove BlobHandler and various calls to .system collection from Solr. This is meant for Solr 10.

Solution

Removals.

Tests

Existing tests only.

Checklist

Please review the following and check all that apply:

• [X ] I have reviewed the guidelines for How to Contribute and my code conforms to the standards described there to the best of my ability.
• [ X] I have created a Jira issue and added the issue ID to my pull request title.
• [X ] I have given Solr maintainers access to contribute to my PR branch. (optional but recommended, not available for branches on forks living under an organisation)
• [ X] I have developed this patch against the main branch.
• [ X] I have run ./gradlew check.
• I have added tests for my changes.
• I have added documentation for the Reference Guide

[gus-asf]

looks like an inadvertent change in one of the doc files, otherwise looks good