optimize Listen bucket notification implementation (#9444)

this commit avoids lots of tiny allocations, repeated
channel creates which are performed when filtering
the incoming events, unescaping a key just for matching.

also remove deprecated code which is not needed
anymore, avoids unexpected data structure transformations
from the map to slice.

cmd/globals.go

@@ -138,6 +138,8 @@ var (
 	globalMinioPort = globalMinioDefaultPort
 	// Holds the host that was passed using --address
 	globalMinioHost = ""
+	// Holds the possible host endpoint.
+	globalMinioEndpoint = ""
 
 	// globalConfigSys server config system.
 	globalConfigSys *ConfigSys