Minor fixes to SDK update PowerShell Script (#8617)
Minor fixes to SDK update PowerShell Script (#8617)

* for Win 7, we need to import BitsTransfer before using it
* switch to PowerShell's build-in archive expander (instead of relying on .NET)
flutter/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,turnidge/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,turnidge/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,turnidge/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,turnidge/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,turnidge/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter