chore(buf): Use nixpkgs-provided buf

The version of buf used is quite old.

nixpkgs provides a more recent version, but it requires us to migrate
config to the latest version.

depot_scanner.proto doesn't honor some of the conventions, so we need
allow_comment_ignores and drop a bunch of comments in there.

Change-Id: Ic978fe92fb7c8471f58c137497528f18aad8f3ab
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7053
Reviewed-by: sterni <sternenseemann@systemli.org>
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: tazjin <tazjin@tvl.su>

buf.yaml

@@ -1,13 +1,12 @@
-build:
-  roots:
-    #- proto
-    - third_party
+version: v1
+
 lint:
-  ignore:
-    - nix/buildGo
+  allow_comment_ignores: true
   use:
     - BASIC
     - FILE_LOWER_SNAKE_CASE
   except:
     - ENUM_VALUE_UPPER_SNAKE_CASE
     - PACKAGE_DIRECTORY_MATCH
+  ignore:
+    - nix/buildGo