* org-agenda.el (org-agenda-collect-markers)
(org-create-marker-find-array): Move to ox-icalendar.el.
(org-agenda-marker-table, org-check-agenda-marker-table):
Delete.
* ox-icalendar.el (org-icalendar-create-uid): New parameter
H-MARKERS to only update some headlines, not the whole file.
(org-icalendar--combine-files): When exporting to an .ics file
only add UID to the headlines shown in the agenda buffer.
(org-agenda-collect-markers, org-create-marker-find-array):
Move here.