Remove unused variables / code (#7736)

* remove unused variables / code

* fix bug in testPostStoreGetOldest

plugin/rpcplugin/muxer.go

@@ -223,7 +223,6 @@ type muxerStream struct {
 	readWake     *sync.Cond
 	isClosed     bool
 	remoteClosed bool
-	closeErr     error
 }
 
 func (s *muxerStream) Read(p []byte) (int, error) {