bird1: Remove, as EOL has been reached

Closes https://github.com/openwrt/routing/issues/993

Deprecation:
https://marc.info/?l=bird-users&m=168682998827356&w=2
https://trubka.network.cz/pipermail/bird-users/attachments/20230615/8517953d/attachment.pdf



Signed-off-by: Marek Küthe <m.k@mk16.de>