I think you do not need, because it is last year and also you are low income, so, no matter you use this T4 or not,you still can get money back. the Gov own you money.
so you just keep this T4, in case somebody chou1 cha2 your tax in the future. but for your case, since you are low income, it will not happend.
I am not sure, just surgesstion, you also can call them and make sure.