Remove abstract RendererFactory and template, category, and attribute renderers.

[kallentu]

Clean up I did a while ago, but I'll cut them into chunks so they're easier to review.

• Removed template, category, and attribute renderers.
• Inlined the renderer work wherever they were used.
• Remove the abstract renderer factory to just use the HTML one.
• Added a comment for future clean up.

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[srawlins]

Excellent!