Remove ca-a and ca-b distinction in test configs #5409

Job	Run time
vendorcheck (1.21.5)	7s
govulncheck (1.21.5)	25s
b (go1.21.5_2023-12-11, ./t.sh --lints --generate)	1m 55s
b (go1.21.5_2023-12-11, ./t.sh --integration && ./test/test-caa-log-checker.sh)	4m 12s
b (go1.21.5_2023-12-11, ./tn.sh --integration)	6m 35s
b (go1.21.5_2023-12-11, ./t.sh --unit --enable-race-detection)	5m 24s
b (go1.21.5_2023-12-11, ./tn.sh --unit --enable-race-detection)	5m 26s
b (go1.21.5_2023-12-11, ./t.sh --start-py)	1m 20s
b (go1.22rc1_2023-12-20, ./t.sh --lints --generate)	42s
b (go1.22rc1_2023-12-20, ./t.sh --integration && ./test/test-caa-log-checker.sh)	4m 15s
b (go1.22rc1_2023-12-20, ./tn.sh --integration)	6m 17s
b (go1.22rc1_2023-12-20, ./t.sh --unit --enable-race-detection)	5m 18s
b (go1.22rc1_2023-12-20, ./tn.sh --unit --enable-race-detection)	5m 28s
b (go1.22rc1_2023-12-20, ./t.sh --start-py)	1m 21s
Boulder CI Test Matrix	1s
	48m 46s

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