Revert "Setting up a way to have uploading by URL, but not on Special:Upload"

Revert "Setting up a way to have uploading by URL, but not on Special:Upload"

This reverts commit 8c6c29b3fc5db93c46bdd73b48f1ff5b4edad25c

I erroneously assumed there was a practical reason why
wgAllowCopyUploads was turned off on Commons, i.e. it was
too easy to abuse, causing too many copyvios, etc. I didn't
realize that the reason it was turned off was purely
technical (since the apaches on the cluster have no
external internet access). So there's no reason we need a
separate config.

Change-Id: I293a59d756335909898fd647edd6eddb68f06e17