Remove duplicated Gutenberg code

There are several instances of code being duplicated from Gutenberg. This is usually because a certain component is not exported.

We should remove all of these, either by making changes in Gutenberg, or modifying the Isolated Block Editor so it doesn't need them.

The issue names no files, tests, or entry points. Start by locating each Gutenberg-derived duplicate in the Isolated Block Editor and determine whether the source component can be exported or the dependency removed. Done means all such duplicates are removed while the affected editor behavior is preserved.

Written by the indexing model from the issue text.