Remove multicol-span-all-margin-nested-003.xht.

It's unclear what it attempted to test. The file name suggests something
with margins, but there are no margins in the test. Furthermore, the ref
assumes a buggy intrinsic width calculation: There are four words of
column content. The max-content-width should be so that the multicol container
can hold all the four words on the same line. There are four columns too, so
the multicol container actually has to be rather wide.

If column-gap is 1em and each character and non-collapsable whitespace
also is 1em wide, the width of the line of text will be 4+1+4+1+4+1+4em
= 19em. That's the column width we want. But we have 4 columns, so
multiply that by 4 -> 76em. Add the 3 gaps between the 4 columns ->
79em. I.e. 1264px if the font-size is 16px. The ref assumes way less
than that (22em).

Bug: 788337
Change-Id: I076af29bf53914557c40b5e438b5eebfb8439e42
Reviewed-on: https://chromium-review.googlesource.com/811645
Reviewed-by: Ian Kilpatrick <[email protected]>
Reviewed-by: Emil A Eklund <[email protected]>
Commit-Queue: Morten Stenshorne <[email protected]>
Cr-Commit-Position: refs/heads/master@{#522164}