Search: remove references to line preview from client code

Created by: camdencheek

Currently, for each line match, we send the content of the line the match belongs to. I'm planning to get rid of that since we'd like matches to be able to span multiple lines, so having a preview of the line that is matched no longer makes sense.

In the web client, getting rid of it is easy because it is never used, so this just deletes any references to it without removing it from the API.

Part of https://github.com/sourcegraph/sourcegraph/issues/31028

Test plan

This seems to be dead code, but am relying on yarn build-ts and existing tests. I did run it locally just to smoke test it.

App preview:

• Web

Check out the client app preview documentation to learn more.