Revert "MDL-36002 core: Make drag and drop keyboard friendly"

This reverts commit 7c271b9, 313e585, ade4695, and 70b4027

Conflicts:
	theme/bootstrapbase/style/moodle.css
MDL-41200 filepicker: change header string to select.
Add length limitation for header, so it fits nicely in mobile devices
MDL-41200 Filepicker: Reduce the string length to fit the dialog size nicely.