Minor fix to the porting guide.
Minor fix to the porting guide.

Removing a line from the porting guide that no longer makes sense.

c64kernal/OpenSubdiv,anshuarya/OpenSubdiv,lookup1980/OpenSubdiv,c64kernal/OpenSubdiv,nyotis/OpenSubdiv,lookup1980/OpenSubdiv,shengfuintel/OpenSubdiv,xldeveloper/OpenSubdiv,c64kernal/OpenSubdiv,takahito-tejima/OpenSubdiv,shengfuintel/OpenSubdiv,shengfuintel/OpenSubdiv,nyotis/OpenSubdiv,takahito-tejima/OpenSubdiv,anshuarya/OpenSubdiv,lookup1980/OpenSubdiv,anshuarya/OpenSubdiv,nyotis/OpenSubdiv,takahito-tejima/OpenSubdiv,xldeveloper/OpenSubdiv,xldeveloper/OpenSubdiv