Revert search in gitignored files in file finder (#4229)

Reverts
https://github.com/zed-industries/zed/pull/3748/commits/2f56fe9129e98520ee9ffbc79c38f0d01ae4ca4d
since gitignored file indexing is inconsistent.

Release Notes:

- Removed the ability to search in gitignored files via file_finder for
now, as it's not consistent enough for good UX