metropolis/pkg/verity: remove unused receiver name

Change-Id: I20416f48c8796601e30d75e42031805841fd242d
Reviewed-on: https://review.monogon.dev/c/monogon/+/3024
Tested-by: Jenkins CI
Reviewed-by: Serge Bazanski <serge@monogon.tech>
Vouch-Run-CI: Tim Windelschmidt <tim@monogon.tech>
diff --git a/metropolis/pkg/verity/encoder_test.go b/metropolis/pkg/verity/encoder_test.go
index db86cd6..116c6a4 100644
--- a/metropolis/pkg/verity/encoder_test.go
+++ b/metropolis/pkg/verity/encoder_test.go
@@ -70,7 +70,7 @@
 
 // Read implements io.Reader on devZeroReader, making it a source of zero
 // bytes.
-func (_ devZeroReader) Read(b []byte) (int, error) {
+func (devZeroReader) Read(b []byte) (int, error) {
 	for i := range b {
 		b[i] = 0
 	}