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_elf.c b/common/cmd_elf.c
index 83e7589..abec7dd 100644
--- a/common/cmd_elf.c
+++ b/common/cmd_elf.c
@@ -313,11 +313,11 @@
 U_BOOT_CMD(
 	bootelf,      2,      0,      do_bootelf,
 	"Boot from an ELF image in memory",
-	" [address] - load address of ELF image.\n"
+	" [address] - load address of ELF image."
 );
 
 U_BOOT_CMD(
 	bootvx,      2,      0,      do_bootvx,
 	"Boot vxWorks from an ELF image",
-	" [address] - load address of vxWorks ELF image.\n"
+	" [address] - load address of vxWorks ELF image."
 );