API Remove silverstripe/campaign-admin integration support #946

Job	Run time
CI / Context	1s
CI / Generate matrix	26s
CI / Check governance	1s
CI / 8.3 prf-low mariadb phpunit all	3m 7s
CI / 8.3 mysql80 phpunit all	3m 11s
CI / 8.3 mysql84 phpunit all	2m 32s
CI / 8.3 mysql80 phplinting	1m 56s
CI / 8.3 mysql80 endtoend root job1	11m 0s
CI / 8.3 mysql80 endtoend root job2	8m 48s
CI / 8.3 mysql80 endtoend root job3	10m 48s
CI / 8.3 mysql80 js	6m 11s
CI / Dispatch tag patch release	0s
	48m 1s

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