SVG: remove |SVGAnimateElement::m_animatedPropertyType|

Before this patch, |SVGAnimateElement::m_animatedPropertyType|
was maintained along |SVGAnimatedTypeAnimator::m_type|,
and there were many ASSERTs checking that they were same.

In this patch, I removed
|SVGAnimateElement::m_animatedPropertyType| and changed
their references to point to
|SVGAnimatedTypeAnimator::m_type| instead.

BUG=378670

Review URL: https://codereview.chromium.org/303093002

git-svn-id: svn://svn.chromium.org/blink/trunk@175245 bbb929c8-8fbe-4397-9dbb-9b2b20218538