net: Remove CMD_PING where there's no CMD_NET

Some boards claim to need ping, but don't support net.
That makes no sense, and causes problems now that ping
is in a separate file.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/include/configs/am3517_crane.h b/include/configs/am3517_crane.h
index 1233985..827a615 100644
--- a/include/configs/am3517_crane.h
+++ b/include/configs/am3517_crane.h
@@ -146,7 +146,7 @@
 #define CONFIG_CMD_MMC		/* MMC support			*/
 #define CONFIG_CMD_NAND		/* NAND support			*/
 #define CONFIG_CMD_DHCP
-#define CONFIG_CMD_PING
+#undef CONFIG_CMD_PING
 
 #undef CONFIG_CMD_FLASH		/* flinfo, erase, protect	*/
 #undef CONFIG_CMD_FPGA		/* FPGA configuration Support	*/