Removed normative dependencies on schemas

[iherman]

Fixes #1566.

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[iherman]

The issue was discussed in a meeting on 2021-03-18

List of resolutions:

• Resolution No. 1: Accept PR 1573

View the transcript

2. Normative Schemas

See github issue #1566.

See github pull request #1573.

Dave Cramer: the quick summary is that epub has historically had some normative schemas
… i think it would be a good idea to change to say that the spec is normative, and that any references to spec are informative only

Matt Garrish: that's part of it
… Ivan particularly didn't like that we were referencing across to epubcheck repo
… basically the PR that we have open now makes that schema section informative, and adds some description boxes to things we hadn't previously defined

Proposed resolution: Accept PR 1573 (Wendy Reid)

Ben Schroeter: +1

Matt Garrish: +1

Toshiaki Koike: +1

Matthew Chan: +1

Masakazu Kitahara: +1

Wendy Reid: +1

Brady Duga: +1

Shinya Takami (高見真也): +1

Resolution #1: Accept PR 1573

Dave Cramer: this makes the distinction between spec and epubcheck clearer, which seems good for everyone