Just delete the expression:
O("kona \\ for help. \\\\ to exit.\n\n");
inside boilerplate function in src/c.c and compile again.
I also removed the initial indentation by removing O(" ") from src/kc.c like this:
(src/kc.c: prompt function, line ~45)
I prompt(I n){ DO(n,O(">")) O(" "); fflush(stdout); R 0; }
to
I prompt(I n){ DO(n,O(">")) fflush(stdout); R 0; }