amdtemp_detach frees dev.cpu.N.temperature oids but leaves dangling entries in the cpu devices' sysctl contexts — latent UAF if a cpu device is ever destroyed

Summary

sc_sysctl_cpu[] oids are allocated in the cpu device's sysctl ctx but detach removes them with sysctl_remove_oid(oid,1,0) without ctx_entry_del on the foreign ctx. Any later sysctl_ctx_free for a cpu device would walk entries pointing at freed oids. Unreachable today (pc64 cpu driver registers no detach); exactly the foot-gun kern_sysctl warns about. ctx-entry-del fix.