PPP, PPPoS, remove magic_randomize() from PPPoS, it is already called in ppp_input()

There is no point of calling magic_randomize() for each pppos_input()
call, making magic_randomize() potentially called for each serial input
byte which is quite a bad idea since magic_randomize() is quite
intensive in processing time (MD5 computation) compared to HDLC frame
parsing. There is no entropy added when being called for each input byte
rather than for each valid input packet because byte input is a
monotonic event at the packet level. Well, if packet arrival time is a
valid entropy source even so, which I doubt a lot, but we don't really
have anything else and we really need random for PPP authentication
layers.

src/netif/ppp/pppos.c

@@ -49,7 +49,6 @@
 
 #include "netif/ppp/ppp_impl.h"
 #include "netif/ppp/pppos.h"
-#include "netif/ppp/magic.h"
 #include "netif/ppp/vj.h"
 
 /* callbacks called from PPP core */
@@ -716,8 +715,6 @@ pppos_input(ppp_pcb *ppp, u8_t *s, int l)
       pppos->in_fcs = PPP_FCS(pppos->in_fcs, cur_char);
     }
   } /* while (l-- > 0), all bytes processed */
-
-  magic_randomize();
 }
 
 #if PPP_INPROC_IRQ_SAFE