chore(common): remove deprecated fields from keyboard_info

Removes the following fields:
* legacyId
* documentationFilename
* documentationFileSize
* links
* related[].note

None of these fields are needed any longer; see #9351 for steps to
remove data.

Eliminates difference between keyboard_info source and distribution,
renaming to keyboard_info.schema.json, and updating the required members
of the json accordingly.

Will have corresponding commits in keyman.com, api.keyman.com,
help.keyman.com, and keyboards repositories.