Remove family provider migrator docs

[sergenyalcin]

Description of your changes

Remove family provider migrator docs because they moved to the new repo

I have:

• Read and followed Crossplane's contribution process.
• Run make reviewable to ensure this PR is ready for review.
• Added backport release-x.y labels to auto-backport this PR if necessary.

[ulucinar]

Thanks @sergenyalcin, lgtm. I think we have already announced the migration docs in this repository and we will need to sync with the community so that they can find the new place for the documentation after the other docs are published and this is merged.

[jeanduplessis]

Thanks @sergenyalcin, lgtm. I think we have already announced the migration docs in this repository and we will need to sync with the community so that they can find the new place for the documentation after the other docs are published and this is merged.

@ulucinar the only places we communicated this to the community are:

• https://docs.google.com/document/d/1tmXi3CRhCKNvdDTApzfNsBIFF88qhpUQth3t5y5oKew/edit
• https://crossplane.slack.com/archives/C056YAQRV16

I can take the action to make the necessary updates to link to the new location.

[ytsarev]

Please mention the new location here :)

[jeanduplessis]

https://github.com/upbound/extensions-migration/tree/main/docs