Clear the line if has_progress_bar (no-op else)

Property definitions

nitc :: testing_base $ ToolContext :: clear_progress_bar
	# Clear the line if `has_progress_bar` (no-op else)
	fun clear_progress_bar
	do
		if has_progress_bar then printn "\r\x1B[K"
	end
src/testing/testing_base.nit:155,2--159,4