Remove incorrect double-escape of quotes in winrm commands

I'm not sure what this line is here to work around, but I found it breaks several commands that I send through winrm.

For example:
```
$env:PATH="$env:PATH;c:\foo"
$env:FOO=$(bar)
```
The quotes on the first line would be double-escaped and the command blows up.

I could not find an example of a command that went wrong after removing this line, provided commands were correctly escaped on the vagrant command line. (For example, by using 'shellescape' in Ruby)