all: fix unused method receiver (syncthing#8988)

refactor: fix unused method receiver

Methods with unused receivers can be a symptom of unfinished refactoring or a bug. To keep 
the same method signature, omit the receiver name or '_' as it is unused.

Co-authored-by: deepsource-autofix[bot] <62050782+deepsource-autofix[bot]@users.noreply.github.com>

Author: deepsource-autofix[bot]

lib/connections/tcp_listen.go

@@ -214,7 +214,7 @@ func (t *tcpListener) Factory() listenerFactory {
 	return t.factory
 }
 
-func (t *tcpListener) NATType() string {
+func (*tcpListener) NATType() string {
 	return "unknown"
 }
 

lib/discover/global_test.go

@@ -241,9 +241,9 @@ func (s *fakeDiscoveryServer) handler(w http.ResponseWriter, r *http.Request) {
 
 type fakeAddressLister struct{}
 
-func (f *fakeAddressLister) ExternalAddresses() []string {
+func (*fakeAddressLister) ExternalAddresses() []string {
 	return []string{"tcp://0.0.0.0:22000"}
 }
-func (f *fakeAddressLister) AllAddresses() []string {
+func (*fakeAddressLister) AllAddresses() []string {
 	return []string{"tcp://0.0.0.0:22000", "tcp://192.168.0.1:22000"}
 }

lib/discover/manager.go

@@ -167,11 +167,11 @@ func (m *manager) Lookup(ctx context.Context, deviceID protocol.DeviceID) (addre
 	return addresses, nil
 }
 
-func (m *manager) String() string {
+func (*manager) String() string {
 	return "discovery cache"
 }
 
-func (m *manager) Error() error {
+func (*manager) Error() error {
 	return nil
 }
 

lib/model/testutils_test.go

@@ -229,7 +229,7 @@ func (c *alwaysChanged) Seen(fs fs.Filesystem, name string) bool {
 	return ok
 }
 
-func (c *alwaysChanged) Changed() bool {
+func (*alwaysChanged) Changed() bool {
 	return true
 }