packagegroup-core-tools-testapps.bb: Remove kexec for riscv32

kexec is not yet ported to riscv32.

Signed-off-by: Mingli Yu <mingli.yu@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit f1e7da77)
Signed-off-by: Anuj Mittal <anuj.mittal@intel.com>