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/barco/barco.c b/board/barco/barco.c
index a19e1ed..d7a0078 100644
--- a/board/barco/barco.c
+++ b/board/barco/barco.c
@@ -307,19 +307,19 @@
 U_BOOT_CMD (
 		try_working, 1, 1, barcobcd_boot_image,
 		"check flash value and boot the appropriate image",
-		"\n"
+		""
 	  );
 
 U_BOOT_CMD (
 		boot_working, 1, 1, barcobcd_boot_image,
 		"check flash value and boot the appropriate image",
-		"\n"
+		""
 	  );
 
 U_BOOT_CMD (
 		boot_default, 1, 1, barcobcd_boot_image,
 		"check flash value and boot the appropriate image",
-		"\n"
+		""
 	  );
 /*
  * We are not using serial communication, so just provide empty functions