selftests/bpf: Remove unused 'key_t' structs

'key_t' is unused in a couple of files since the original commit 60dd49ea
("selftests/bpf: Add test for bpf array map iterators"). Remove it.
Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240602234112.225107-3-linux@treblig.org

tools/testing/selftests/bpf/progs/bpf_iter_bpf_array_map.c

@@ -6,12 +6,6 @@
 
 char _license[] SEC("license") = "GPL";
 
-struct key_t {
-	int a;
-	int b;
-	int c;
-};
-
 struct {
 	__uint(type, BPF_MAP_TYPE_ARRAY);
 	__uint(max_entries, 3);

tools/testing/selftests/bpf/progs/bpf_iter_bpf_percpu_array_map.c

@@ -6,12 +6,6 @@
 
 char _license[] SEC("license") = "GPL";
 
-struct key_t {
-	int a;
-	int b;
-	int c;
-};
-
 struct {
 	__uint(type, BPF_MAP_TYPE_PERCPU_ARRAY);
 	__uint(max_entries, 3);