Bug#1084410: s3backer: move from fuse to fuse3

[Bastian Germann]

Control: forwarded -1 
https://github.com/archiecobbs/s3backer/commit/104afdf062bff490b4ca4ccd7e6ce70b7c6eb641
Control: tags -1 upstream fixed-upstream

This was released with v2.1.5. Please import that or a newer release.