Fixed slow tokenizer behavior to make it remove special tokens when asked

[pedrogengo]

What does this PR do?

Fixes #23250

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[HuggingFaceDocBuilderDev]

The docs for this PR live here. All of your documentation changes will be reflected on that endpoint.

[amyeroberts]

cc @ArthurZucker

[pedrogengo]

I still need to do some more tests, but the idea is just add the special in the special tokens list. I will work more on it in this week :)

[ArthurZucker]

Hey! Thanks for working on this and good luck haha! Ping me if you need any help on fixing the tests.
I think that the core bug is gonna be bit tricky to get right, but it should be fixed

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