[Installer] Delete the old files during refresh
[Installer] Delete the old files during refresh

Fixes the issue where, after refreshing, the new files wouldn't be
copied over because of the check that prevents clobbering files.

perl6/modules.perl6.org,perl6/modules.perl6.org,perl6/modules.perl6.org,perl6/modules.perl6.org,masak/proto,masak/proto,masak/proto