Repair step to remove "photo." files created by photocache

Before https://github.com/nextcloud/server/pull/13843

 a "photo." file could be created
for unsupported image formats by photocache. Because a file is present but not jpg, png or gif no
photo could be returned for this vcard. These invalid files are removed by this repair step.

Signed-off-by: Daniel Kesselberg <mail@danielkesselberg.de>