meta-agl-bsp: remove old Raspberry Pi U-Boot recipe

meta-agl-bsp: remove old Raspberry Pi U-Boot recipe

Newer U-Boot recipes were added to pick up the 4B support, remove
the older ones since they are no longer used.

Bug-AGL: SPEC-4072

Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Change-Id: Iedc9b7ec189316319296d2a23c0293559e83566c
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/26778
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
(cherry picked from commit 54a20427a2c553165ce9a8393aeda218e7aa310e)
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/26803