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/mpl/mip405/cmd_mip405.c b/board/mpl/mip405/cmd_mip405.c
index dc13804..cd93a7c 100644
--- a/board/mpl/mip405/cmd_mip405.c
+++ b/board/mpl/mip405/cmd_mip405.c
@@ -60,7 +60,7 @@
 	"mip405 flash mps - updates U-Boot with image from MPS\n"
 	"mip405 info      - displays board information\n"
 	"mip405 led <on>  - switches LED on (on=1) or off (on=0)\n"
-	"mip405 mem [cnt] - Memory Test <cnt>-times, <cnt> = -1 loop forever\n"
+	"mip405 mem [cnt] - Memory Test <cnt>-times, <cnt> = -1 loop forever"
 );
 
 /* ------------------------------------------------------------------------- */