[Nealtw]

I would use a diamond blade in an angle grinder and cut straight down flush with the wall about 1/2" deep.
Then i would use a rotary hammer with a chisel to knock it down lower than the floor, and then use cement product to fill it up level.

 

[Nealtw]

According to your level, you may be able to use SLC on the floor to even it out with the cmu. Fill the holes in the cmu and smooth it all out.

You must be one of those retired guys