Block Editor: Remove non-public fetchSearchSuggestions from LinkControl documentation

[aduth]

Previously: #19705 (comment)

This pull request seeks to resolve an issue where the LinkControl component is documented to support a fetchSearchSuggestions prop. However, this prop was removed as of #19705 under the assumption it was not expected to be needed (after #19638).

That said, there's two approaches this could take:

• Reintroduce the prop to the component
• Remove the documented prop

The current pull request changes implement the second option.

It is not clear to me whether this prop is actually needed, or if it's sufficient to rely on the __experimentalFetchLinkSuggestions block settings value which is select-ed in the internal implementation of the component. It may have been useful previously for the purpose of the unit tests to verify the expected behavior of a stubbed fetch function.

Testing Instructions:

Currently, the only changes are to the documentation, so there are no expected changes to the application runtime.

[youknowriad]

Thanks