meta-agl-core: remove rng-tools bbappend

meta-agl-core: remove rng-tools bbappend

The rng-tools patches are now being applied in the upstream recipe in
dunfell 3.1.6, so the local bbappend and patches can now be dropped.

Bug-AGL: SPEC-3840

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: Id431d9e5259fd78d6f36934ed4839ef4aa35ba2b
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/26146
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Reviewed-by: Julien Massot <julien.massot@iot.bzh>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
(cherry picked from commit 743d2973ad2f70af0301ac4667e0ebb4ef2b1bf1)
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/26164
Tested-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>