Revert "Workaround dojox.form.BusyButton bug in dojo 1.9.0"

This reverts commit 716d975dee0fb81c7feaf6fc8d418ea4ff5329aa.
Get rid of dojox/form/BusyButton for now

The previous workaround did not work out as expected.
A ticket has been filled in dojo bug tracking system:
https://bugs.dojotoolkit.org/ticket/17205