Added raw_reaction_remove in paginator.

[Cryptex-github]

Added reaction_remove in paginator so you don't have to click twice to go the next page.

Rationale

The reason behind this change is because I find it is annoying to click twice to go to the next page I believe it will benefit to users because I do believe most people don't like to click twice to go to the next page.

Summary of changes made

I used asyncio.ensure_future and asyncio.wait to wait for either event to be fired.

Checklist

• [x] This PR changes the jishaku module/cog codebase
  • [x] These changes add new functionality to the module/cog
  • [ ] These changes fix an issue or bug in the module/cog
  • [x] I have tested that these changes work on a production bot codebase
  • [ ] I have tested these changes against the CI/CD test suite
  • [ ] I have updated the documentation to reflect these changes
• [ ] This PR changes the CI/CD test suite
  • [ ] I have tested my suite changes are well-formed (all tests can be discovered)
  • [ ] These changes adjust existing test cases
  • [ ] These changes add new test cases
• [ ] This PR changes prose (such as the documentation, README or other Markdown/RST documents)
  • [ ] I have proofread my changes for grammar and spelling issues
  • [ ] I have tested that any changes regarding Markdown/RST syntax result in a well formed document

[scarletcafe]

I get the practicality rationale of this change, but I am worried it may be confusing.

At the very least, I would still prefer that the bot removes reactions itself if it can do so. To keep compatibility with this change in such a case, the check would need to be adjusted to ensure the bot ignores its own reaction removals in the case that the bot's permissions change while an interface is open (or maybe just to ignore bots outright - I am not sure why it doesn't do this already).

[scarletcafe]

Over the course of the last couple of commits, I've redesigned the update and event retrieval mechanics of PaginatorInterface. This takes this design change into account.

I wanted to get the bot removing the reaction itself if possible, but it turns out such events do not give any information to suggest the reaction wasn't removed by the user themselves. I guess one thing I could do is check channel permissions and change between the two behaviors based on whether the bot can or not, but I'd prefer to stay consistent so I'll leave it as is with removals considered and change it if I get complaints later.