General help message cleanup

Many of the help messages were not really helpful; for example, many
commands that take no arguments would not print a correct synopsis
line, but "No additional help available." which is not exactly wrong,
but not helpful either.

Commit ``Make "usage" messages more helpful.'' changed this
partially. But it also became clear that lots of "Usage" and "Help"
messages (fields "usage" and "help" in struct cmd_tbl_s respective)
were actually redundant.

This patch cleans this up - for example:

Before:
	=> help dtt
	dtt - Digital Thermometer and Thermostat

	Usage:
	dtt         - Read temperature from digital thermometer and thermostat.

After:
	=> help dtt
	dtt - Read temperature from Digital Thermometer and Thermostat

	Usage:
	dtt

Signed-off-by: Wolfgang Denk <wd@denx.de>
diff --git a/board/esd/cpci405/cpci405.c b/board/esd/cpci405/cpci405.c
index ccbe245..a677c62 100644
--- a/board/esd/cpci405/cpci405.c
+++ b/board/esd/cpci405/cpci405.c
@@ -690,8 +690,8 @@
 U_BOOT_CMD(
 	onewire,	1,	1,	do_onewire,
 	"Read 1-write ID",
-	NULL
-	);
+	""
+);
 
 #define CONFIG_SYS_I2C_EEPROM_ADDR_2 0x51 /* EEPROM CAT24WC32 */
 #define CONFIG_ENV_SIZE_2 0x800 /* 2048 bytes may be used for env vars */
@@ -751,8 +751,8 @@
 U_BOOT_CMD(
 	getbpip,	1,	1,	do_get_bpip,
 	"Update IP-Address with Backplane IP-Address",
-	NULL
-	);
+	""
+);
 
 /*
  * Set and print backplane ip...
@@ -787,7 +787,7 @@
 U_BOOT_CMD(
 	setbpip,	2,	1,	do_set_bpip,
 	"Write Backplane IP-Address",
-	NULL
-	);
+	""
+);
 
 #endif /* CONFIG_CPCI405AB */