rtos: remove remains of old XTOS spinlock.h implementation #21222

Job	Run time
LP64-WIP	3m 51s
manifest-check	1m 1s
build-linux (mnfst, ptl)	4m 31s
build-linux (mnfst, tgl tgl-h)	4m 47s
build-linux (mnfst, imx8 imx8x imx8m imx8ulp)	5m 33s
build-linux (mnfst, mtl lnl)	5m 4s
build-linux (zmain, imx8 imx8x imx8m imx8ulp)	5m 5s
build-linux (mnfst, --all)	4m 56s
build-linux (zmain, ptl)	1m 58s
build-linux (zmain, tgl tgl-h)	2m 4s
build-windows (imx8 imx8x imx8m imx8ulp)	5m 55s
build-linux (-d, mnfst, lnl)	2m 19s
build-windows (-d, lnl)	3m 46s
build-windows (tgl tgl-h)	3m 10s
build-windows (ptl)	2m 7s
build-linux (zmain, mtl lnl)	1m 48s
build-windows (mtl lnl)	1m 35s
compare-linux-win	24s
	59m 54s

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