Do not show useless "Description:" label in entity type doc boxes

The “type” attribute of an entity (for example: Opera is a type of Work) has a description. That description is displayed in the help bubble next to its editing field only for works and all other entity types since MBS-11163.

Possible improvements:

1. Drop the “Description:” label as that seems to be unneeded.
2. Make phrasing less convoluted, for example, start with “An opera is… is not…” instead of “This represents an opera…”.
3. Display a list of descriptions for all type attributes of the same entity type, for users to compare between them to select the most appropriate one, e.g. https://musicbrainz.org/doc/Release_Group/Type