Revert "scripts/download: add sources CDN as first mirror"

This reverts commit c737a9ee6a9c47b6e553ac81bf293b1161e59799.

The source CDN has been discontinued in its current form and will take a
while to be reestablished. Even then it makes little sense to put a CDN
before other CDNs such as kernel.org, apache.org, sourceforge etc.

Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit bf96eb55c82191701030b68810e6f19adbb91eeb)

scripts/download.pl

@@ -258,7 +258,6 @@ foreach my $mirror (@ARGV) {
 	}
 }
 
-unshift @mirrors, 'https://sources.cdn.openwrt.org';
 #push @mirrors, 'https://mirror1.openwrt.org';
 push @mirrors, 'https://sources.openwrt.org';
 push @mirrors, 'https://mirror2.openwrt.org/sources';