docs(snix/docs/TODO): drop fetchGit/fetchTree TODO

Migrated to #126.

Change-Id: Iccfc0cbd9bdc08fde337ae097eb7ddb57c67d439
Reviewed-on: https://cl.snix.dev/c/snix/+/30472
Reviewed-by: Jonas Chevalier <zimbatm@zimbatm.com>
Autosubmit: Florian Klink <flokli@flokli.de>
Tested-by: besadii

snix/docs/src/TODO.md

@@ -70,14 +70,6 @@ Extend the other pages in here. Some ideas on what should be tackled:
    is probably still not too clear.
  - Absorb the rest of //snix/website into this.
 
-## Features
-
-### Fetchers
-Some more fetcher-related builtins need work:
- - `fetchGit`
- - `fetchTree` (hairy, seems there's no proper spec and the URL syntax seems
-   subject to change/underdocumented)
-
 ### Derivation -> Build
 While we have some support for `structuredAttrs` and `fetchClosure` (at least
 enough to calculate output hashes, aka produce identical ATerm), the code