Revert "HTML output: add 'id' attribute foreach event"

This reverts commit d218fdc27b.

Because an event has no id:

    Event = namedtuple('Event', ['talk', 'row', 'rowcount'])

cfp/planning.py

@@ -151,7 +151,6 @@ class Program:
                     if event.row != 0:
                         continue
                     options = ' rowspan="%d" bgcolor="%s"' % (event.rowcount, event.talk.category.color)
-                    options += ' id="%d"' % event.id
                     cellcontent = escape(str(event.talk)) + '<br><em>' + escape(event.talk.get_speakers_str()) + '</em>'
                     if self.staff:
                         tags = event.talk.staff_tags