Fix bug on non-default system drives

[Carterpersall]

win10debloat.ps1:

• Closes #206, Any reference to C: prevents compatibility with systems that use other drives for their system, this fixes that by replacing all references to C: with $env:SystemDrive

Much of this was previously in my pull request #285 but there were issues with the diff creating confusion that caused it to be closed. So I'm redoing everything and putting them all into separate pull requests to increase clarity on exactly what has changed.

[Carterpersall]

The upcoming update will probably break this, please don't close it though as I intend to fix it for the update.