As in bug 1659363, Google calendar puts HTML tags in the DESCRIPTION of calendar events for formatting (bold, italic, etc.). This doesn't exactly follow the iCalendar spec where DESCRIPTION is plain text.
So for readability, when we are displaying descriptions in read-only contexts, we should strip out the HTML tags and just show the text content. Bug 1659363 took care of invitations in emails; this bug is for the event/todo summary dialog and ICS file import dialog.
(In the edit event dialog where the description is editable we should show the actual raw contents of the description property, i.e. include the HTML tags.)