Remove lines allowing clippy cognitive complexity checks.

Since these allow lines were added, this clippy lint has been downgraded
to a nursery check via
rust-lang/rust-clippy#5428

Since we don't have allows for other nursery lints, I suggest we remove
these ones.

mp4parse/tests/public.rs

@@ -44,7 +44,6 @@ static AVIF_CORRUPT_IMAGES: &str = "tests/corrupt";
 
 // Adapted from https://github.com/GuillaumeGomez/audio-video-metadata/blob/9dff40f565af71d5502e03a2e78ae63df95cfd40/src/metadata.rs#L53
 #[test]
-#[allow(clippy::cognitive_complexity)] // TODO: Consider simplifying this
 fn public_api() {
  let mut fd = File::open(MINI_MP4).expect("Unknown file");
  let mut buf = Vec::new();
@@ -164,7 +163,6 @@ fn public_api() {
 }
 
 #[test]
-#[allow(clippy::cognitive_complexity)] // TODO: Consider simplifying this
 fn public_metadata() {
  let mut fd = File::open(MINI_MP4_WITH_METADATA).expect("Unknown file");
  let mut buf = Vec::new();
@@ -231,7 +229,6 @@ fn public_metadata() {
 }
 
 #[test]
-#[allow(clippy::cognitive_complexity)] // TODO: Consider simplifying this
 fn public_metadata_gnre() {
  let mut fd = File::open(MINI_MP4_WITH_METADATA_STD_GENRE).expect("Unknown file");
  let mut buf = Vec::new();
@@ -529,7 +526,6 @@ fn public_audio_cbcs() {
 }
 
 #[test]
-#[allow(clippy::cognitive_complexity)] // TODO: Consider simplifying this
 fn public_video_cbcs() {
  let system_id = vec![
  0x10, 0x77, 0xef, 0xec, 0xc0, 0xb2, 0x4d, 0x02, 0xac, 0xe3, 0x3c, 0x1e, 0x52, 0xe2, 0xfb,
@@ -610,7 +606,6 @@ fn public_video_cbcs() {
 }
 
 #[test]
-#[allow(clippy::cognitive_complexity)] // TODO: Consider simplifying this
 fn public_video_av1() {
  let mut fd = File::open(VIDEO_AV1_MP4).expect("Unknown file");
  let mut buf = Vec::new();

mp4parse_capi/tests/test_encryption.rs

@@ -12,7 +12,6 @@ extern "C" fn buf_read(buf: *mut u8, size: usize, userdata: *mut std::os::raw::c
 }
 
 #[test]
-#[allow(clippy::cognitive_complexity)] // TODO: Consider simplifying this
 fn parse_cenc() {
  let mut file = std::fs::File::open("tests/short-cenc.mp4").expect("Unknown file");
  let io = Mp4parseIo {