fs/streams: Move the file streams from the group structure into TLS

This is preparation for flushing streams from user space, like it should
be done.

- Move tg_streamlist (group, kernel space) ->
       ta_streamlist (TLS, user space)
- Access stream list via tg_info in kernel
- Access stream list via TLS in user space
- Remove / rename nxsched_get_streams -> lib_getstreams
- Remove system call for nxsched_get_streams

syscall/syscall.csv

@@ -74,7 +74,6 @@
 "nx_pthread_exit","nuttx/pthread.h","!defined(CONFIG_DISABLE_PTHREAD)","noreturn","pthread_addr_t"
 "nx_vsyslog","nuttx/syslog/syslog.h","","int","int","FAR const IPTR char *","FAR va_list *"
 "nxsched_get_stackinfo","nuttx/sched.h","","int","pid_t","FAR struct stackinfo_s *"
-"nxsched_get_streams","nuttx/sched.h","defined(CONFIG_FILE_STREAM)","FAR struct streamlist *"
 "open","fcntl.h","","int","FAR const char *","int","...","mode_t"
 "pgalloc", "nuttx/arch.h", "defined(CONFIG_BUILD_KERNEL)", "uintptr_t", "uintptr_t", "unsigned int"
 "pipe2","unistd.h","defined(CONFIG_PIPES) && CONFIG_DEV_PIPE_SIZE > 0","int","int [2]|FAR int *","int"