Refactor VPN configuration handling to remove device limit management

- Updated the VPN configuration commands and handlers to eliminate the device limit parameter, simplifying the configuration process.
- Adjusted related API documentation to reflect the removal of device limit management, clarifying that this setting is now handled directly in the 3x-ui by node administrators.
- Enhanced the overall codebase by removing unnecessary device limit references across various components, ensuring a cleaner and more maintainable code structure.

backend/tests/PnvPanel.Application.Tests/Configs/Revoke/RevokeVpnConfigCommandHandlerTests.cs

@@ -23,7 +23,7 @@ public class RevokeVpnConfigCommandHandlerTests
 
         var node = Node.Register("node-1", new Uri("https://node1.example.com"), new NodeCredentials("admin", "protected"), null);
         var inbound = Inbound.FromRemote(node.Id, "1", VpnProtocol.Vless, "remark", 443);
-        var config = VpnConfig.Create(userId, inbound.Id, VpnProtocol.Vless, null, 0);
+        var config = VpnConfig.Create(userId, inbound.Id, VpnProtocol.Vless, null);
         config.AssignRemoteClient("external-id");
 
         dbContext.Nodes.Add(node);
@@ -49,7 +49,7 @@ public class RevokeVpnConfigCommandHandlerTests
         var userId = Guid.NewGuid();
 
         var inbound = Inbound.FromRemote(Guid.NewGuid(), "1", VpnProtocol.Vless, "remark", 443);
-        var config = VpnConfig.Create(userId, inbound.Id, VpnProtocol.Vless, null, 0);
+        var config = VpnConfig.Create(userId, inbound.Id, VpnProtocol.Vless, null);
         config.Revoke();
 
         dbContext.Inbounds.Add(inbound);