Remove all delimiters between opener and closer

Property definitions

markdown2 $ MdInlineParser :: remove_delimiters_between
	# Remove all delimiters between `opener` and `closer`
	private fun remove_delimiters_between(opener, closer: nullable MdDelimiter) do
		if opener == null or closer == null then return

		var delimiter = closer.prev
		while delimiter != null and delimiter != opener do
			var previous_delimiter = delimiter.prev
			remove_delimiters_keep_node(delimiter)
			delimiter = previous_delimiter
		end
	end
lib/markdown2/markdown_inline_parsing.nit:1016,2--1026,4