ekf2: remove legacy accel z bias checks #24555

Job	Run time
build (check_format)	1m 11s
build (tests)	5m 36s
build (tests_coverage)	6m 55s
build (px4_fmu-v2_default stack_check)	3m 10s
build (validate_module_configs)	51s
build (shellcheck_all)	1m 33s
build (NO_NINJA_BUILD=1 px4_fmu-v5_default)	4m 10s
build (NO_NINJA_BUILD=1 px4_sitl_default)	3m 21s
build (px4_sitl_allyes)	4m 17s
build (airframe_metadata)	1m 5s
build (module_documentation)	1m 3s
build (parameters_metadata)	1m 3s
	34m 15s

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