Revert "Combobox: Set role='combobox' on input element (#2756)" (#2972)

* Revert "Combobox: Set role='combobox' on input element (#2756)"

This reverts commit 2b249fc.

# Conflicts:
#	components/combobox/__docs__/__snapshots__/storybook-stories.storyshot
#	components/combobox/__tests__/combobox.browser-test.jsx
#	components/combobox/combobox.jsx
#	components/component-docs.json
#	components/date-picker/__tests__/__snapshots__/datepicker.dom-snapshot-test.jsx.snap

* Update snapshots

* Remove double roles

Author: interactivellama