ical-recurrence: fold the duplicated recurEvents test groups into one
ICal.RecurrenceSpec had grown two `describe "recurEvents"` blocks, the
second defining `calendarWith`, `startsOf` and `utcAt` all over again,
plus a second `describe "RecurrenceDateTimes"` and a second
`describe "ExceptionDateTimes"` alongside their twins.
That is an artefact of how these tests arrived: each was written against a
version of the file that did not have the block yet, and rebasing replayed
the block along with the test. Nothing caught it, because a duplicate
`describe` and a shadowed `let` are both perfectly legal, so the suite
stayed green while the fixtures diverged.
It is not only untidy. A test written into the second block cannot see
the `zurich` and `plusOne` helpers defined in the first, which is a
confusing way to find out that the file has two of everything.
No test is added, removed or renamed by this: the set of test names before
and after is identical, and the suite stays at 260 passing.