More raw cleanup

[shainaraskas]

This PR does some content cleanup that allows me to remove some stray raw files:

• moved the shard request cache doc into the distributed architecture section (context)
• deleted a file where the content was moved into a draft (http apis)
• cleaned up the start/stop request routing topic to apply to both ECH and ECE, moved it out of the ECE section, deleted the raw ECH file (fixes https://github.com/elastic/docs-projects/issues/440)
• removed some upgrade-related files that are used up

[bmorelli25]

The context link in the description doesn't work for me. Assuming your context is correct, this LG