Warn for uploads with new name but same content as local file

Warn for uploads with new name but same content as local file

Previously warnings about the sha1 of an uploaded file being
the same as an existing file were stripped if the existing
file was in local storage - this was to avoid duplicate
warnings if a file with the same name had already been found
and had the same content. Now the warning is only stripped
for local files with the same name as the uploaded file.

Bug: T180691
Change-Id: I455df30085c05320dca976b9f7f8fb711a083271