refactor(tvix/cli/args): remove log-level argument

RUST_LOG allows for a more granular tracing configuration

Change-Id: Iea29fc2b154345eb7479dfd8bbea6abfd4716341
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12585
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

tvix/docs/src/TODO.md

@@ -262,9 +262,6 @@ This requires some more designing. Some goals:
 - Some work ongoing on the worker operation parsing (griff, picnoir)
 
 ### O11Y
- - Maybe drop `--log-level` entirely, and only use `RUST_LOG` env exclusively?
-   `debug`,`trace` level across all crates is a bit useless, and `RUST_LOG` can
-   be much more granular…
  - Trace propagation for object_store once they support a way to register a
    middleware, so we can use that to register a tracing middleware.
    https://github.com/apache/arrow-rs/issues/5990