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/common/cmd_universe.c b/common/cmd_universe.c
index bfb91b5..0a6d722 100644
--- a/common/cmd_universe.c
+++ b/common/cmd_universe.c
@@ -382,5 +382,5 @@
 	"                                      03 -> Configuration Space\n"
 	"    [vdw] = VMEbus Maximum Datawidth: 01 -> D8 Data Width\n"
 	"                                      02 -> D16 Data Width\n"
-	"                                      03 -> D32 Data Width\n"
+	"                                      03 -> D32 Data Width"
 );