[chromium] Optimize expectaions for fast/forms/button-generated-content.html

Unreviewed gardening.

* platform/chromium-win-xp/fast/forms/button-generated-content-expected.png: Removed.
* platform/chromium-win/fast/forms/button-generated-content-expected.png:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@139301 268f45cc-cd09-0410-ab3c-d52691b4dbfc