text: Title: Tidy up oembed_providers.py
  Body: ### Issue Summary
  
  Currently [oembed_providers.py](https://github.com/wagtail/wagtail/blob/ac38343957787b7d7a2ff34164a98538e177ff96/wagtail/embeds/oembed_providers.py) has a list of providers that no longer exist. A quick example would be Revision3.com, it longer exists as a service.
  
  ### Steps to Reproduce
  
  ```
  from wagtail.embeds.embeds import get_embed
  get_embed('http://www.revision3.com/demo')
  ```
  
  Returns an `EmbedNotFoundException` exception, but there's other exceptions underneath because the URL/hostname doesn't exist.
  
  Not a huge issue, but if there's a dead provider that isn't accepting connections - it just hangs:
  
  ```
  get_embed('http://qik.com/demo')
  ```
  
  -   I have confirmed that this issue can be reproduced as described on a fresh Wagtail project: yes
  
  ### Technical details
  
  -   Python version: Any
  -   Django version: Any
  -   Wagtail version: 6.1 / main
  -   Browser version: n/a
  
  ### Working on this
  
  I think this is probably a "good first issue", so would love to see someone else give this one a go.