Remove the last bracket on the last_bracket stack

Property definitions

markdown2 $ MdInlineParser :: remove_last_bracket
	# Remove the last bracket on the `last_bracket` stack
	private fun remove_last_bracket do
		var last_bracket = self.last_bracket
		if last_bracket == null then return
		self.last_bracket = last_bracket.prev
	end
lib/markdown2/markdown_inline_parsing.nit:639,2--644,4