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_jffs2.c b/common/cmd_jffs2.c
index 3bb6c3c..4db4a83 100644
--- a/common/cmd_jffs2.c
+++ b/common/cmd_jffs2.c
@@ -636,18 +636,17 @@
 	"load binary file from a filesystem image",
 	"[ off ] [ filename ]\n"
 	"    - load binary file from flash bank\n"
-	"      with offset 'off'\n"
+	"      with offset 'off'"
 );
 U_BOOT_CMD(
 	ls,	2,	1,	do_jffs2_ls,
 	"list files in a directory (default /)",
-	"[ directory ]\n"
-	"    - list files in a directory.\n"
+	"[ directory ]"
 );
 
 U_BOOT_CMD(
 	fsinfo,	1,	1,	do_jffs2_fsinfo,
 	"print information about filesystems",
-	"    - print information about filesystems\n"
+	""
 );
 /***************************************************/