Hidden beneath the crush of gas tax, gun bills and death penalty repeal that the Maryland General Assembly is wrestling with this year are smaller ones that don’t get much notice. And as time grows short, many of them die. The measure, which would have forbidden landlords to discriminate against tenants based on their source of income, had occupied hours of the Senate’s time when Senator James Rosapepe, a College Park Democrat, moved to send it back to the committee where it originated, essentially killing the bill.