[css-fonts-3] Fix trailing whitespace in test-synthetic-italic.xht

[mrego]

This was introduced in cb0aa48.

@svgeesus introduced this trailing whitespace by mistake, and it's causing Tavis failures (e.g. https://travis-ci.org/w3c/csswg-test/jobs/185842710).

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This change is 

[syncbot]

Automatic validation checks of commit 33af162 passed.

[mrego]

I hope it's fine to merge this unreviewed, as I'm just fixing Travis CI.

[Ms2ger]

Thanks for fixing.

[frivoal]

How could @svgeesus 's commit land in the repo if it breaks travis, and you cannot merge anything unless travis is happy with it? Was this done via hg? I thought we were closing down write access to the hg side of the mirror.

[Ms2ger]

People were still able to push to master directly; I think I fixed that.

[frivoal]

Thanks.