Copter: cleanup EKF failsafe units and division #28081

Job	Run time
build (chibios, Durandal)	17m 6s
build (chibios, MatekF405)	14m 41s
build (chibios, KakuteF7)	13m 25s
build (chibios, MatekH743-bdshot)	16m 39s
build (chibios, Pixhawk1-1M)	15m 27s
build (chibios, MatekF405-CAN)	2m 0s
build (chibios, DrotekP3Pro)	3m 6s
build (chibios, Hitec-Airspeed)	3m 29s
build (chibios, f103-GPS)	3m 32s
build (disco, armhf)	14m 21s
	1h 43m 46s

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