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/ssv/common/cmd_sled.c b/board/ssv/common/cmd_sled.c
index 99ff507..449c1a4 100644
--- a/board/ssv/common/cmd_sled.c
+++ b/board/ssv/common/cmd_sled.c
@@ -157,6 +157,6 @@
 
 U_BOOT_CMD (sled, 3, 0, do_sled,
 	    "check and set status led",
-	    "sled [name [state]]\n" __NAME_STR "    - state: on|off|blink\n");
+	    "sled [name [state]]\n" __NAME_STR "    - state: on|off|blink");
 #endif
 #endif	/* CONFIG_STATUS_LED */