Remove some duplicate newlines in call to wfDebug()

Spotted on beta:

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commonswiki-375c0c3e:

0.0752   1.9M  mime: <image/png> extension: <png>

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With lot of requests, that causes them to be interlayed and ungreppable.

Change-Id: Ib99bc9547bdecb9efa59b7d292ddd7d10a552652