Latex Paint won't come off
Painter here.  If paint doesn't want to leave the surface, I generally don't ask it to.  I just paint over it.  

Deep colors are a PiTA to paint over if your ultimate destination is an off-white (like most all housepaint). The key is to use a primer with high opacity and hit it with several coats until it is covered and the surface looks uniform.  Primer is cheaper than paint and is better suited to coverup surfaces of differing colors and textures. 

The biggest problem you get laying it down uniform is that the roller doesn't put it down evenly.  That will be disturbingly apparent on the first coat, but don't give up.  The second coat will be much better, as the color will only punch through where both coats happen to be thin. Coat #3 will be vastly better still.  Somewhere around 3 or 4 you will reach "good enough".