ScheduledTask - using the Credential, and Removing an existing Job

the DSC resource was failing in the LCM with Access-Denied, so I plumbed
the Credential into the Set-TargetResource function and used it with
New-PSSession (same pattern I saw in Test-TargetResource)
removing a line of dead code
Merge pull request #2 from craig-martin/master

Fix for ScheduledTask - existing Job, and using Credentials