Hey there, I'd say, these receipts are not REALLY necessary for the app to work and do its job, BUT they serve as a way for the app (and macOS) to know what's installed and what's not in terms of Sound Library content.
If receipts are removed, Logic may assume that you don't have any content installed. Though, you'd still be able to load the library sounds and presets, no problem, because patches and presets are stored together with the library content or in ~/Music/Audio Music Apps/ folder, so this functionality won't be affected. Also Apple Loops won't be affected, either. Loops database is stored in ~/Music/Audio Music Apps/Databases folder (and before LPX 10.5.1 loops index files had been stored inside the app bundle itself).
The real issue, as I see it, after removing the receipts Logic's Sound Library Manager won't be of any use if you'll later want to relocate the library to external drive. But then again, a solution is simply to reinstall the library (not that much of hassle with download speeds these days).
In addition, not sure how Logic itself might react when you launch it for the first time after removing the receipts. It may just go business as usual, or it may force Library content re-download on you (which will render the whole exercise useless).
P.S. Experiment with receipts at your own risk. If you'd like to learn more on advanced techniques of Logic's library management, you may want to explore this thread: https://www.logicprohelp.com/forum/topic/122990-reinstalling-logic-x-with-existing-sound-library/#comment-704547 (especially stuff by user "jth4")