Remove default labels from issue templates

[tetrapod00]

Why:

• Many reporters don't understand exactly what we consider a "bug" or an "enhancement" for the docs. If a user tries to do something, look for information in the docs, and can't find what they need, that sure feels like a bug, even if we consider missing information to be an enhancement.
• The line between the two is a bit fuzzy for the docs. A lot of the time, I see an issue that should probably be an enhancement rather than a bug, but it's not a big enough deal to change the label.
• Issues starting with a label makes it difficult to filter the list of issues for untriaged and unlabeled issues.
• Keeps consistency with the other Godot repos, where a new issue starts out totally unlabeled, and it is up to issue triagers to determine the appropriate labels.

Personally, when triaging docs issues I would much rather start from an empty list of labels than a potentially incorrect single label.

I'd like to hear what other frequent triagers think. CC @AThousandShips @skyace65

[skyace65]

No disagreements from me

[AThousandShips]

Makes sense to me, makes it easier to identify new issues (though we allow people to tag their issues so that's less critical)

[mhilbrunner]

In this goes then. Thanks, and thanks everyone for chiming in! ⛄