When installing from the PG Music USB drive to a hard drive on your computer (which you don't have to do), yes, you will get both a .WMA and a .WAV of each sound but you just need one or the other to use that sound.
Yes, you could write a batch file to go through and remove all the .WMA files if you wanted, but I don't think it's worth the effort since they are only 1/11 the size of the .WAV files.
Likewise, to save space, you could delete some .WAV files of sounds you don't plan to use, but you would have to do that manually within each folder you choose, which would take quite some effort.
What I do instead is use a file manager and copy only the folders that are new each year that I know I want from the USB drive over to my hard drive. And I bought a hard drive just for RealTracks and RealDrums.
BIAB 2021 Win Audiophile & 2020 Mac UltraPak. Software: Studio One 5 Pro, Adobe Audition CC, Notion 6; Win 10 64 Pro. Hardware: custom i7 16 Gb; Roland Integra-7, Presonus Studio 192, Presonus Faderport 8, Royer 121, Adam sub & monitors