Remove old upgrade logic

[nickoferrall]

We previously refactored our upgrade to team tier logic. Now we have the oldUpgradeToTeamTier mutation, which we should remove.

But before removing it, the DiscussPhaseSqueeze and InsightDomainNudge components, use the credit card modal which uses the old upgrade logic.

To remove the oldUpgradeTeamTier mutation, we'll need to either refactor the credit card modal to use the new mutation, or direct users towards the /billing page.

AC

• [ ] Old upgradeToTeamTier mutation is safely removed