AP_ROMFS: remove requirement that returned buffer is null-terminated #35586

Job	Run time
build (stm32f7, chibios, 10)	3m 58s
build (stm32h7, chibios, 10)	3m 35s
build (fmuv2-plane, chibios, 10)	2m 14s
build (periph-build, chibios, 10)	5m 18s
build (iofirmware, chibios, 10)	1m 38s
build (CubeOrange-bootloader, chibios, 10)	50s
build (fmuv3-bootloader, chibios, 10)	1m 10s
build (revo-bootloader, chibios, 10)	52s
build (stm32h7-debug, chibios, 10)	2m 37s
build (fmuv3, chibios, 10)	5m 32s
build (revo-mini, chibios, 10)	4m 23s
build (MatekF405-Wing, chibios, 10)	4m 25s
build (CubeOrange-ODID, chibios, 10)	2m 33s
build (CubeRedPrimary-bootloader, chibios, 10)	1m 10s
build (configure-all, chibios, 10)	9m 15s
build (build-options-defaults-test, chibios, 10)	6m 13s
build (signing, chibios, 10)	2m 45s
build (CubeOrange-PPP, chibios, 10)	2m 13s
build (CubeOrange-SOHW, chibios, 10)	2m 26s
build (Pixhawk6X-PPPGW, chibios, 10)	1m 24s
	1h 4m 31s

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