Is it possible to install unmodified, unadulterated and pure Android on a Sony Xperia S?
Of course you can

Just pick one from all the available ROMS, you will find some vanilla builds there if you only want the basics. But it requires the knowledge of rooting your ROM and flashing

if you are afraid of flashing but not rooting, then you can just remove the apps that you don't want using Titanium backup.