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/pcs440ep/pcs440ep.c b/board/pcs440ep/pcs440ep.c
index 9cc3f5b..47d6391 100644
--- a/board/pcs440ep/pcs440ep.c
+++ b/board/pcs440ep/pcs440ep.c
@@ -763,7 +763,7 @@
 	"              0x02 = DIAG 2 on\n"
 	"              0x04 = DIAG 3 on\n"
 	"              0x08 = DIAG 4 on\n"
-	"              > 0x100 set the LED, who are on, to state blinking\n"
+	"              > 0x100 set the LED, who are on, to state blinking"
 );
 
 #if defined(CONFIG_SHA1_CHECK_UB_IMG)
@@ -823,7 +823,7 @@
 	"calculate the SHA1 Sum",
 	"address len [addr]  calculate the SHA1 sum [save at addr]\n"
 	"     -p calculate the SHA1 sum from the U-Boot image in flash and print\n"
-	"     -c check the U-Boot image in flash\n"
+	"     -c check the U-Boot image in flash"
 );
 #endif