Removes common code

[MiYanni]

Description

Removes the common code that is now in azure-powershell-common.

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• The appropriate change log has been updated
• The PR does not introduce breaking changes
• If applicable, the changes made in the PR have proper test coverage
• For public API changes to cmdlets:
  • the changes have gone through a cmdlet design review
  • the cmdlet markdown files were generated using the platyPS module

[MiYanni]

Jobs:
sign: https://azuresdkci.westus2.cloudapp.azure.com/view/PowerShell/job/ps-sign/1140/
netsign: https://azuresdkci.westus2.cloudapp.azure.com/view/PowerShell/job/psnetsign/147/
demand: https://azuresdkci.westus2.cloudapp.azure.com/view/PowerShell/job/powershell-demand/1072/