Revert "std.c: add netbsd's accept_filter_data for ACCEPT_FILTER sock opt."

This reverts commit b677b36278.

lib/std/c/netbsd.zig

@@ -485,11 +485,6 @@ pub const AF = struct {
     pub const MAX = 37;
 };
 
-pub const accept_filter_arg = extern struct {
-    af_name: [16]u8,
-    af_args: [240]u8,
-};
-
 pub const in_port_t = u16;
 pub const sa_family_t = u8;