etcd: remove (unused) etcd root bucket prefix

This commit removes the unused prefix from the etcd backend config as
etcd key space separation in LND is implemented by using namespaces
instead.

config.go

@@ -1398,10 +1398,6 @@ func (c *Config) localDatabaseDir() string {
 		lncfg.NormalizeNetwork(c.ActiveNetParams.Name))
 }
 
-func (c *Config) networkName() string {
-	return lncfg.NormalizeNetwork(c.ActiveNetParams.Name)
-}
-
 // CleanAndExpandPath expands environment variables and leading ~ in the
 // passed path, cleans the result, and returns it.
 // This function is taken from https://github.com/btcsuite/btcd