Old concrete "patch" on basement wall - what to do with it?

[Galen Bricker]

I am flipping a house that a previous owner smeared a bunch of concrete on a part of the basement wall. I assume they were trying to keep water from coming into the house but it didn't help.  I fixed the real problem but now I'm left with this ugly concrete patch on the basement wall.  I painted the wall but it still sticks out.  The biggest complaint that I get from buyers is this patch.  They are afraid that it is hiding something or there is a problem.  It is stuck tight and I can't remove it.  Any ideas what to do with this?