meta-yocto: Delete PREFERRED_VERSION for obsolete version of U-Boot.
The OE recipe for U-Boot v2013.07 was deleted in 2014, so remove this
reference to it.
(From meta-yocto rev: a864e357f8d02ba52a38a96fd8b03f01c60888e8)
Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Robert P. J. Day