Remove unused ScrollAnimatorNone::PerAxisData constructor argument.

The 'parent' argument is not used, remove it.

This implicitly fixes an incorrect invocation of the constructor from
ScrollAnimatorNoneTest::SavePerAxisData, which following r183583 was
passing in an uninitialized pointer value as argument.

R=mkwst
BUG=

Review URL: https://codereview.chromium.org/648273002

git-svn-id: svn://svn.chromium.org/blink/trunk@183625 bbb929c8-8fbe-4397-9dbb-9b2b20218538