[NDIS] NdisRegisterProtocol(): Add a comment about NDIS51 (#8314)

CORE-20300

- `NdisRegisterProtocol()`: Add a comment about `NDIS51`: the
  `NDIS50_PROTOCOL_CHARACTERISTICS` structure is common to both
  NDIS 5.0 and 5.1.
  This is in contrast to the `NDIS50/NDIS51_MINIPORT_CHARACTERISTICS`
  structures, see for example commit 3e169e3cb2 (r49961).

- Remove obsolete SOURCES file. Addendum to commit d9e83ed22d (r40142).

drivers/network/ndis/ndis/SOURCES

@@ -1,15 +0,0 @@
-TARGETNAME=ndis
-TARGETPATH=obj
-TARGETTYPE=EXPORT_DRIVER
-
-C_DEFINES=-DNDIS_WRAPPER=1 -DNDIS50=1 -DNDIS51=1 -DNDIS50_MINIPORT=1 -DNDIS51_MINIPORT=1
-
-INCLUDES=..\include;..\..\..\..\include;..\..\..\..\include\reactos
-
-SOURCES= 40gone.c 50gone.c buffer.c cl.c cm.c co.c config.c control.c \
-         efilter.c hardware.c io.c main.c memory.c miniport.c protocol.c \
-         string.c stubs.c time.c
-
-MSC_WARNING_LEVEL=/W3 /WX
-
-DLLDEF=$(O)/ndis.def

drivers/network/ndis/ndis/protocol.c

@@ -1156,6 +1156,7 @@ NdisRegisterProtocol(
       break;
 
     case 0x05:
+      /* Identical for both NDIS50 and NDIS51 */
       MinSize = sizeof(NDIS50_PROTOCOL_CHARACTERISTICS);
       break;