symbolic icons: clean up sheet

- some duplicate bounding boxes
- misaligned boxes caused fuzzy icon export (needs to snap to grid)
- some icons elements overlapped the bounding box, creating icons larger than 16x16
- nested groups with duplicate label name
- all objects need to be outline only (no strokes)

Fixes #1677
1 job for wip/jimmac/gtk4-symbolic-icons in 60 minutes and 8 seconds (queued for 1 second)
latest