common: Discard the __u_boot_cmd section

The command declaration now uses the new LG-array method to generate
list of commands. Thus the __u_boot_cmd section is now superseded and
redundant and therefore can be removed. Also, remove externed symbols
associated with this section from include/command.h .

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Joe Hershberger <joe.hershberger@gmail.com>
Cc: Mike Frysinger <vapier@gentoo.org>

board/pb1x00/u-boot.lds

@@ -54,12 +54,6 @@ SECTIONS
 
 	.sdata  : { *(.sdata*) }
 
-	.u_boot_cmd : {
-	  __u_boot_cmd_start = .;
-	  *(.u_boot_cmd)
-	  __u_boot_cmd_end = .;
-	}
-
 	. = ALIGN(4);
 	.u_boot_list : {
 		#include <u-boot.lst>