testutil/registry: remove unused WithStdout(), WithStErr() opts

These were added as part of d7ba1f85ef,
but weren't used at the time, and still aren't used, so let's remove
them.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

testutil/registry/ops.go

@@ -1,7 +1,5 @@
 package registry
 
-import "io"
-
 // Schema1 sets the registry to serve v1 api
 func Schema1(c *Config) {
 	c.schema1 = true
@@ -26,17 +24,3 @@ func URL(registryURL string) func(*Config) {
 		c.registryURL = registryURL
 	}
 }
-
-// WithStdout sets the stdout of the registry command to the passed in writer.
-func WithStdout(w io.Writer) func(c *Config) {
-	return func(c *Config) {
-		c.stdout = w
-	}
-}
-
-// WithStderr sets the stdout of the registry command to the passed in writer.
-func WithStderr(w io.Writer) func(c *Config) {
-	return func(c *Config) {
-		c.stderr = w
-	}
-}