Why did Apple Music duplicate my .mp3 songs into .m4a?

A few months ago I had to restore my entire music library using the .mp3 files on an external hard drive.

A few days ago I noticed all of my songs were duplicated in iTunes match.

I had two versions of every song in iTunes, so I deleted all of the ones labeled "Matched" under Cloud Status. Now, when I browse to my songs on my hard drive, there is an .mp3 version (which I want iTunes to use) and an .m4a version.

What happened and how do I quickly remove all .m4a versions from my hard drive? Why does Apple Music keep duplicating files? I'm at my wit's end with Apple Music and it's weird duplication that keeps happening. Below is an image: