Update first responder examples to use new context location.

[davidlehn]

The first responder context was moved to fr-spec repo and hosted there. Examples should be updated to point to the new location.

At least used here:

• https://github.com/credential-handler/vc-examples/tree/main/credentials/fr-medical-technician

Context may be able to be removed, but may be in use by issued examples. If not removed, should add a readme with comment that this is depreacted now.

• https://github.com/credential-handler/vc-examples/tree/main/contexts/first-responder

See:

• Update contexts. digitalbazaar/fr-spec#3
• Update first-responder redirects. perma-id/w3id.org#4811

[BigBlueHat]

Context may be able to be removed, but may be in use by issued examples. If not removed, should add a readme with comment that this is depreacted now.

Yeah, we'll add a deprecation notice, but not remove it. I want this space (and most/all other context spaces) to act as immutable stores...Git(Hub) plumbing to make it act that way TBD.