kernel-devsrc: remove symlink source

kernel-devsrc: remove symlink source

Fixed:
$ rpm -qplv tmp/deploy/rpm/qemuppc/kernel-devsrc-1.0-r0.qemuppc.rpm | grep kernel/source
/usr/src/kernel/source -> /buildarea/lyang1/test_yocto/tmp/work/qemuppc-poky-linux/kernel-devsrc/1.0-r0/image/usr/src/kernel

It is generated by kernel's "make clean _mrproper_scripts", the
kernel-devsrc includeds full sources, this symlink is not needed, and
the path is invalid on target, so remove it.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>