rtos: remove remains of old XTOS spinlock.h implementation #21253

Job	Run time
manifest-check	56s
LP64-WIP	3m 57s
build-windows (mtl lnl)	8m 32s
build-windows (imx8 imx8x imx8m imx8ulp)	9m 42s
build-windows (tgl tgl-h)	8m 50s
build-linux (zmain, tgl tgl-h)	5m 51s
build-linux (mnfst, imx8 imx8x imx8m imx8ulp)	6m 41s
build-linux (-d, mnfst, lnl)	4m 43s
build-windows (ptl)	7m 33s
build-linux (mnfst, --all)	16m 42s
build-linux (zmain, ptl)	4m 35s
build-linux (zmain, mtl lnl)	5m 53s
build-linux (mnfst, ptl)	4m 53s
build-linux (mnfst, mtl lnl)	6m 3s
build-linux (zmain, imx8 imx8x imx8m imx8ulp)	6m 33s
build-linux (mnfst, tgl tgl-h)	5m 54s
build-windows (-d, lnl)	6m 29s
compare-linux-win	1m 54s
	1h 55m 41s

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