Remove RenderTheme::supportsDataListUI.

The purpose of the funciton was to describe support differences between desktop
platforms and Android. Android Chrome now supports same input types for
<datalist>. We don't need the function any longer.

Note for BaseMultipleFieldsDateAndTimeInputType::createShadowSubtree:
|shouldAddPickerIndicator| is always true. We can remove it.

BUG=none
TEST=none; no behaivor changes.

Review URL: https://codereview.chromium.org/181013012

git-svn-id: svn://svn.chromium.org/blink/trunk@168603 bbb929c8-8fbe-4397-9dbb-9b2b20218538