3.0 Deprecation Warning: Remove deprecated tokenizers

[ancalita]

Background
This warning was found in:

• rasa.nlu.tokenizers.convert_tokenizer:L27
• rasa.nlu.tokenizers.lm_tokenizer.py:L21

"f""'{self.__class__.__name__}' is deprecated and ""
f""will be removed in the future. ""
f""It is recommended to use the '{WhitespaceTokenizer.__name__}' or ""
f""another {Tokenizer.__name__} instead."","

Definition of Done

• resolve warnings in 3.0 version
• Removed the deprecated tokenizers from the codebase.
• Added a changelog entry for 3.0 saying we've removed the previously deprecated tokenizers
• Removed the references in the docs

[samsucik]

Are we actually removing these tokenisers in 3.0? 🤔

[kedz]

Also removing deprecated featurization related to the LanguageModelTokenizer originally from this issue #8879 :

• rasa.nlu.utils.hugging_face.hf_transformers.py