mkelfimage: Remove un-needed recipe

mkelfimage: Remove un-needed recipe

As we are removing the ELF image type, we can now removed this older
mkelfimage recipe also, we reach back 3+ years in the coreboot git repo
to retrieve the source.  This tool needs updating everything we change
binutils, which would normally be done by the upstream, but that is now
gone.

[YOCTO #11967]

(From OE-Core rev: 003056db591ebee6464b51d29f706779936fcd83)

Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>