CLOUDSTACK-9315: Removed unused Classes (#1448)

* Remove some unused Classes

These classes were deleted because they have no references in our code base. They are not in Spring execution flow nor instantiated with "new":
- com.cloud.agent.api.CheckStateAnswer
- com.cloud.agent.api.StartupVMMAgentCommand
- com.cloud.agent.api.routing.UserDataCommand
	- remove from description at
com.cloud.configuration.Config.ExecuteInSequenceNetworkElementCommands
enum
- com.cloud.agent.api.storage.UpgradeDiskCommand
- com.cloud.agent.api.storage.CreatePrivateTemplateCommand
- com.cloud.agent.api.storage.DestroyAnswer
	- Note: "FIXME: Should have an DestroyAnswer" at
com.cloud.storage.resource.StoragePoolResource
- com.cloud.agent.api.storage.UpgradeDiskAnswer
- com.cloud.agent.api.storage.ManageVolumeAvailabilityAnswer
- com.cloud.agent.api.storage.ManageVolumeAvailabilityCommand
- com.cloud.exception.UsageServerException
- com.cloud.info.SecStorageVmLoadInfo
- com.cloud.serializer.SerializerHelper

* PR#1448 update description of 'execute.in.sequence.network.element.commands' param

Update description of 'execute.in.sequence.network.element.commands'parameter to reflect an unused command that has been removed. The removed class command is 'UserDataCommand'.

* Add cloud schema to update SQL

Author: GabrielBrascher