That adhesive is supposed to be there, it isn't a problem. That stuff doesn't get dissolved by rubbing alcohol or acetone either so you haven't damaged anything
Well there is the the greater issue Intel's normal manufacturing process uses (used) glue and thermal paste to connect the heat spreader to the die instead of solder; which you can learn more about if you read up on how/why people delid processors. But bottom line is your processor is fine and it's probably been like that the entire time without you noticing.
For what it's worth, that CPU doesn't look delided to me. Usually the black adhesive gets replaced with a red silicone when people do that