build/fietsje: remove

We've moved back to using go.mod as a source of truth, as our main large
depdency (Kubernetes) is now mostly gomod compatible.

Change-Id: Ie6215b7330a7dcec7681fa3081437efb2be5bf77
Reviewed-on: https://review.monogon.dev/c/monogon/+/651
Reviewed-by: Lorenz Brun <lorenz@monogon.tech>
diff --git a/BUILD b/BUILD
index d9121bb..8244c90 100644
--- a/BUILD
+++ b/BUILD
@@ -5,9 +5,14 @@
 # gazelle:go_naming_convention import
 gazelle(name = "gazelle")
 
-alias(
-    name = "fietsje",
-    actual = "//build/fietsje/cmd",
+gazelle(
+    name = "gazelle-update-repos",
+    args = [
+        "-from_file=go.mod",
+        "-to_macro=third_party/go/repositories.bzl%go_repositories",
+        "-prune",
+    ],
+    command = "update-repos",
 )
 
 # Shortcut for the Go SDK