Pandoc used to emit a `header` class on the `tr` element that forms the table header. This is no longer needed, because `head > tr` will do the same thing.
Similarly, pandoc used to emit `even` and `odd` classes on `tr`s, allowing striped styling. This is no longer needed, because one can use e.g. `tbody tr:nth-child(2n)`.
We now omit these classes, which have a good chance of conflicting with classes used for other things.
Closes#9325.
ThomasSoeiro