Remove obsolete references to licensing from functions-and-operators docs page

Since we changed the way licensing works (throttling vs gatekeeping features), our functions page needs to remove all references to licensing.

Page to be changed: https://www.cockroachlabs.com/docs/stable/functions-and-operators

Some of the functions have the following comment:

```
This function requires an enterprise license on a CCL distribution.
```

These sentences can all be removed. There are 9 of them in total.

Jira issue: DOC-16126