Two of the largest Medicare Advantage insurers in the US, UnitedHealthcare and Humana, have signaled in recent days that they plan to exit certain “underperforming” markets and curb benefits in an effort to boost their bottom lines, a strategy that’s expected to kick more than a million seniors from their coverage.On Thursday, Axios cited an analyst note published earlier this week indicating that UnitedHealthcare “has dropped around 13% of plan…