It is not mandatory, but you will lose lot's of basic stuff such as: plugin name, ability to (really) disable the plugin, Q2A and PHP version checks, plugin version update checks, among others.
You could move that to the qa-plugin.php file but that behavior is deprecated and you won't be able to disable the plugin anyway, if you do so.
Considering it is just a single and considerable small file, it makes no sense at all to take any action on that.