In ghci, how to remove an existing binding?

I am getting a "binding shadows the existing binding" error similar to the one from this question.

Prelude Api.Facility Control.Monad.IO.Class> let t = getBadgesNot 1 (Nothing) (Just 1)

<interactive>:55:5: warning: [-Wname-shadowing]
    This binding for ‘t’ shadows the existing binding
      defined at <interactive>:39:5

I defined the existing binding earlier in the session, and am now trying to redefine it. Is there a way to remove the existing binding so that I can redefine t?

I notice that in other circumstances ghci does not error when redefining an existing binding. For example

Prelude> let t = 1
Prelude> let t = 2
Prelude> let t = "there"

Why does ghci error when redefining an existing binding in some cases and not in others?