API Remove silverstripe/campaign-admin integration support #1719

Job	Run time
CI / Context	1s
CI / Generate matrix	14s
CI / Check governance	0s
CI / 8.3 prf-low mariadb phpunit all	2m 40s
CI / 8.3 mysql80 phpunit all	2m 53s
CI / 8.3 mysql84 phpunit all	2m 37s
CI / 8.3 mysql80 phplinting	2m 11s
CI / 8.3 mysql80 endtoend root job1	10m 26s
CI / 8.3 mysql80 endtoend root job2	8m 9s
CI / 8.3 mysql80 endtoend root job3	9m 2s
CI / 8.3 mysql80 js	5m 58s
CI / Dispatch tag patch release	0s
	44m 11s

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