[#1189] node/config: Fix `PersistentSessionsConfig.Path` method's docs

Method never returns `PersistentStatePathDefault` value, and this is
correct.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

cmd/neofs-node/config/node/config.go

@@ -153,8 +153,6 @@ func PersistentSessions(c *config.Config) PersistentSessionsConfig {
 }
 
 // Path returns the value of "path" config parameter.
-//
-// Returns PersistentStatePathDefault if the value is not a non-empty string.
 func (p PersistentSessionsConfig) Path() string {
 	return config.String(p.cfg, "path")
 }