use new PointOnSurface of tilemaker instead of custom shapefile

[oberhamsi]

this can now be replaced https://github.com/shortbread-tiles/shortbread-tilemaker/blob/main/boundary_labels_shape_file.md since tilemaker v3 added PointToSurface

see https://github.com/systemed/tilemaker/blob/eab08d189ad97ddf5db7d915bcabe42ad3dab6af/CHANGELOG.md?plain=1#L13 and ticket https://github.com/systemed/tilemaker/issues/392

i can try to prepare a PR

[joto]

@oberhamsi Yes, PR would be great!