API Remove silverstripe/campaign-admin integration support #1016

Job	Run time
CI / Context	1s
CI / Generate matrix	20s
CI / Check governance	0s
CI / 8.3 prf-low mariadb phpunit all	3m 15s
CI / 8.3 mysql80 phpunit all	3m 4s
CI / 8.3 mysql84 phpunit all	3m 4s
CI / 8.3 mysql80 phplinting	2m 4s
CI / 8.3 mysql80 endtoend root job1	9m 30s
CI / 8.3 mysql80 endtoend root job2	8m 38s
CI / 8.3 mysql80 endtoend root job3	6m 48s
CI / 8.3 mysql80 js	4m 51s
CI / Dispatch tag patch release	0s
	41m 35s

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