[$] Splicing out vmsplice()

The splice()and vmsplice()system calls are meant to improve performance for certain data-movementtasks by minimizing (or avoiding altogether) system calls and the copyingof data. They also have a long history of security problems. The recentflood of LLM-discovered vulnerabilities has drawn attention, once again, tosplice() and vmsplice(); as a result, they may end upbeing removed altogether.