Remove photo prefix from every exif property name

Summary:
Remove the 'photo' prefix from every exif property,
as this is pretty redundant
CCBUG: 343273

Reviewers: ngraham, bruns

Reviewed By: ngraham

Subscribers: kde-frameworks-devel, #baloo

Tags: #frameworks, #baloo

Differential Revision: https://phabricator.kde.org/D21772