Simplify grails-doc-core tests

[jdaugherty]

Issue description

The the grails-doc-core project has an entire copy of the generated documentation. I can't see a reason this is needed, we only need to test a subset of the html. Alternatively, we could add tests to the grails-doc project and test the tasks under that one on the real, generated documentation.

Because grails-gradle/docs-core/src/test/resources has so many html files, it's causing 66% of our project to look like it's html. We need to remove this directory / come up with a simpler test solution.

[jdaugherty]

I've removed some of these files, but the single.html needs reduced to some basic examples.

[jdaugherty]

It has been decided we'll remove PDF publishing support from our HTML doc generation. This will also fix the licensing issues that were found.