When using nextcloud, before this change we only uploaded one of SHA1
or MD5 checksum in the OC-Checksum header with preference to SHA1 if
both were set.
This makes the MD5 checksums read as empty string which makes syncing
with checksums less useful than they should be as all the MD5
checksums are blank.
This change makes it so that we only upload the SHA1 to nextcloud.
The behaviour of owncloud is unchanged as owncloud uses the checksum
as an upload integrity check only and calculates its own checksums.
See: https://forum.rclone.org/t/how-to-specify-hash-method-to-checksum/13055
4fbc90d115