remove the old versions of the utility function and use the new

src/RIGID/fix_rigid.cpp

@@ -2302,7 +2302,7 @@ void FixRigid::readfile(int which, double *vec,
   int nread = 0;
   while (nread < nlines) {
     nchunk = MIN(nlines-nread,CHUNK);
-    eofflag = comm->read_lines_from_file(fp,nchunk,MAXLINE,buffer);
+    eofflag = utils::read_lines_from_file(fp,nchunk,MAXLINE,buffer,me,world);
     if (eofflag) error->all(FLERR,"Unexpected end of fix rigid file");
 
     buf = buffer;