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_flash.c b/common/cmd_flash.c
index f1f3517..9f27ab0 100644
--- a/common/cmd_flash.c
+++ b/common/cmd_flash.c
@@ -712,7 +712,7 @@
 	flinfo,    2,    1,    do_flinfo,
 	"print FLASH memory information",
 	"\n    - print information for all FLASH memory banks\n"
-	"flinfo N\n    - print information for FLASH memory bank # N\n"
+	"flinfo N\n    - print information for FLASH memory bank # N"
 );
 
 U_BOOT_CMD(
@@ -726,7 +726,7 @@
 	"erase N:SF[-SL]\n    - erase sectors SF-SL in FLASH bank # N\n"
 	"erase bank N\n    - erase FLASH bank # N\n"
 	TMP_ERASE
-	"erase all\n    - erase all FLASH banks\n"
+	"erase all\n    - erase all FLASH banks"
 );
 
 U_BOOT_CMD(
@@ -751,7 +751,7 @@
 	"    - make sectors SF-SL writable in FLASH bank # N\n"
 	"protect off bank N\n    - make FLASH bank # N writable\n"
 	TMP_PROT_OFF
-	"protect off all\n    - make all FLASH banks writable\n"
+	"protect off all\n    - make all FLASH banks writable"
 );
 
 #undef	TMP_ERASE