docs: fix typos (#19024)

Co-authored-by: zeertzjq <zeertzjq@outlook.com>
Co-authored-by: Valery Viktorovsky <viktorovsky@gmail.com>

src/nvim/fileio.c

@@ -5270,7 +5270,6 @@ void forward_slash(char_u *fname)
     return;
   }
   for (p = fname; *p != NUL; p++) {
-    // The Big5 encoding can have '\' in the trail byte.
     if (*p == '\\') {
       *p = '/';
     }