Remove backoff extension from docs template #333

Job	Run time
static	3m 17s
test (docs)	3m 0s
test (examples)	2m 32s
test (test, test local var val, --test-arg --test-arg)	1m 4s
test (remote, 0)	2m 58s
test (remote-test, remote-test, 1)	3m 7s
test (test-coverage, test local var val, --test-arg, test-coverage)	1m 18s
test (test-coverage, test local var val, --test-arg, 3.8, ubuntu-20.04, test-coverage-oldest)	1m 7s
test (test-nengo, test local var val, --test-arg, 3.11)	1m 14s
coverage	17s
auto-update	2m 9s
deploy	0s
	22m 3s

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