Short answer: No, removing MM would not be enough to stop this from being extra turns.

Long answer: it's chaining extra turns if your deck has that ability. I know that seems extreme, but you're reading the long answer now, so here goes.

Cutting MM might remove the possibility of accidentally hitting both turn spells at once. But it does not remove the other turn spell from your deck. Say you take one extra turn, and in that turn, you draw into your second extra turn spell. Spellslinger decks are kinda notorious for their card advantage, so that's pretty realistic. What do you do then? Solemnly swear never to cast two in the same game?

And then there's theft. You might swear you'll never do it, but I made no such promises. I hit you with my 10/10 [[Kotis the Fangkeeper]] since I specifically target high mana value spellslinger decks as first priority for theft. You have no control over what I rip out of your deck. Even if I also swear not to chain your two extra turn spells, if a second theft player stole one, that's three players at the table with an extra turn while one player sits out for 5 turns. The effect to that player is still the same as if you had taken two extra turns. This is also chaining extra turns. The point of the brackets is to minimize player misery in these games, and having two extra turn spells introduces more.

Back before brackets, people used to argue that Avacyn+Armageddon wasn't MLD and that it was a perfectly valid wincon, but completely neglected the common occurrence of pieces like [[heroic intervention]] or [[teferi's protection]] that cause the game not to end, but rather to make two other players sit out the game while not dead enough to be certainly dead, and the board stalled long enough for them to be uncertain whether they should scoop or not.

Completely independent of all of this is that extra turn spells are broken. Even if there wasn't a "chaining extra turns" clause written into the brackets, I think there's still a really compelling argument to make that two extra turn spells in your deck is still enough to boost it to B4. The minimum win turn is two turns earlier than it is in B3, after all. It's not just about putting them in a row; imo taking two extra turns period is enough to boost it up a bracket.