Backport #20855
Whilst looking at #20840 I noticed that the Mirrors data doesn't appear
to be being used therefore we can remove this and in fact none of the
related code is used elsewhere so it can also be removed.
Related #20840
Related #20804
Signed-off-by: Andrew Thornton <art27@cantab.net>
Signed-off-by: Andrew Thornton <art27@cantab.net>
Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>