Involved in the second step of GPI biosynthesis. De-N-acetylation of N-acetylglucosaminyl-phosphatidylinositol (By similarity). a 6-(N-acetyl-alpha-D-glucosaminyl)-1-phosphatidyl-1D-myo-inositol + H2O = acetate + an alpha-D-GlcN-(1->6)-(1,2-diacyl-sn-glycero-3-phospho)-1D-myo-inositol Glycolipid biosynthesis; glycosylphosphatidylinositol-anchor biosynthesis. Belongs to the PIGL family.