Docs: Remove olm.bundle.mediatype FBC property and plain+v0 bundle support

[joelanford]

User story

As a maintainer of OLMv1, I want to remove support for the prototype plain+v0 bundle type and other related code so that I can decrease the surface area of OLMv1 for its eventual GA release.

Epic Link

#818

List the user-facing issues in the epic that require documentation.

• Issue: Remove plain+v0 support from ClusterExtension #823

Does this epic require new content or updates to existing content?

• Net-new content
• Update existing content

What type of documentation is required for this epic?

• Release note
• Concept
• Procedure
• Reference

Is there prior art or reference materials that would help write the documentation?

Documentation should be contributed to the docs/drafts/ directory

[michaelryanpeter]

/assign

[michaelryanpeter]

I have searched the repo for references to the plain bundle docs. I think that this ticket can safely be closed.