Revert Kog'Maw back to pre-marksmen update

I feel like a lot of the challenge late game with positioning has been removed with his w update. It's simply too strong and feels slightly spammy. I understand a large part of the update was because of his lack of popularity, but this lack of popularity was due to his lack of mobility in a mobility based meta at the time not due to being under powered. On the other hand that lack of mobility was what made him fun for the few that did play him. And there was a specific comp designed around him (we all know Protect-the-kog). This proves he was strong enough, as with a comp like that he usually soared.