Minor clean-up around unused arguments

[Benglin]

Background

This pull request is meant to standardize the way DynamoModel is shutdown (more specifically, RevitDynamoModel).

Changes

Existing shutdown behavior

Shutdown sequence 1 (an ideal scenario):

1. DynamoView.WindowClosing > RevitDynamoModel.ShutDown
2. RevitDynamoModel.ShutDown > IdlePromise.ExecuteOnShutdown
3. RevitDynamoModel.ShutDown > DynamoModel.ShutDown
4. DynamoModel.ShutDown
5. RevitDynamoModel.ShutDown > IdlePromise.ExecuteOnIdleAsync (PostableCommand.ExitRevit)
6. DynamoRevit.DynamoView_Closing > IdlePromise.ClearPromises 
7. DynamoRevit.DynamoView_Closing > IdlePromise.Shutdown
8. DynamoRevit.DynamoView_Closed
9. Shutdown delegate (from Step #2 above)

Shutdown sequence 2 (incorrect scenario):

1. DynamoView.WindowClosing > RevitDynamoModel.ShutDown
2. DynamoRevit.DynamoView_Closing > IdlePromise.ClearPromises 
3. DynamoRevit.DynamoView_Closing > IdlePromise.Shutdown
4. DynamoRevit.DynamoView_Closed
5. RevitDynamoModel.ShutDown > IdlePromise.ExecuteOnShutdown
6. RevitDynamoModel.ShutDown > DynamoModel.ShutDown
7. DynamoModel.ShutDown
8. RevitDynamoModel.ShutDown > IdlePromise.ExecuteOnIdleAsync (PostableCommand.ExitRevit)
9. Shutdown delegate NOT executed (#5 comes after #3) 

ShutDown sequence 3:

1. DynamoRevit.DynamoView_Closed

There are various ways a shutdown sequence can be initiated:

1. Pressing X button on Dynamo window (sequence 1)
2. By update manager (sequence 2)
3. File > Exit menu item (sequence 2)
4. Closing Revit main window (sequence 3)

[sharadkjaiswal]

@Benglin DO NOT MERGE pull request is merged :)

[Benglin]

No worries, @sharadkjaiswal, more changes into this "major" branch has not taken place so its content is exactly the same as Clean-up of DynamoModel.ShutDown methods (which has already been reviewed/merged in). I'll make another new pull request.