This change removes the Lucene's experimental flag from the documentations of the following
tokenizer/filters:

• Simple Pattern Split Tokenizer
• Simple Pattern tokenizer
• Flatten Graph Token Filter
• Word Delimiter Graph Token Filter

The flag is still present in Lucene codebase but we're fully supporting these tokenizers/filters
in ES for a long time now so the docs flag is misleading.

• Have you signed the contributor license agreement?
• Have you followed the contributor guidelines?
• If submitting code, have you built your formula locally prior to submission with gradle check?
• If submitting code, is your pull request against master? Unless there is a good reason otherwise, we prefer pull requests against master and will backport as needed.
• If submitting code, have you checked that your submission is for an OS and architecture that we support?
• If you are submitting this code for a class then read our policy for that.