Do not re-apply labels every time somebody makes an rfcbot command?

[nagisa]

See for example https://github.com/rust-lang/rust/pull/51230#issuecomment-399214953 after which labels appear to be added again even though they were never removed.

[Centril]

I must say I am surprised that GitHub even reapplies labels... It seems like a bug on their part.

Seems like something we should fix on our end tho; we can do it with the naive approach of checking if a label is applied before applying it again (or perhaps with some more ratelimit friendly approach...).

However; this will have to wait a bit as I think there are more pressing features to add and such.

But I will get around to it eventually.