[windows] Fix downloading dependencies from mirrors

[Montellese]

Description

This reverts commit de42ae8 see #13293
As mentioned in the comments in the commit it breaks downloading dependencies from any mirror which does not return the Location HTTP header. Furthermore it invalidates the value of ERRORLEVEL which now contains the return code of findstr instead of from wget.

Motivation and Context

When setting up my Windows 10 dev machine I noticed that lots of windows dependency downloads failed randomly and I had to restart download-dependencies.bat alot until I got all dependencies. Now when I setup the new windows build slave I ran into the same problem again. I then realized that from the 11 mirrors I tried

• 8 did not return the Location HTTP header
• 1 (https://ftp.halifax.rwth-aachen.de/xbmc/) uses a self-signed HTTPS certificate. Maybe @kib can comment on this?

which leads to the download being considered as failed (for the second reason that's correct).

This should also be backported to Leia since it was introduced there and will also lead to build failures there.

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• None of the above (please explain below)

Checklist:

• My code follows the Code Guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the Contributing document
• I have added tests to cover my change
• All new and existing tests passed