Fix a few new clippy warnings

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-rs/-/merge_requests/1120>

net/aws/src/s3sink/imp.rs

@@ -84,18 +84,14 @@ impl Started {
     }
 }
 
+#[derive(Default)]
 enum State {
+    #[default]
     Stopped,
     Completed,
     Started(Started),
 }
 
-impl Default for State {
-    fn default() -> State {
-        State::Stopped
-    }
-}
-
 struct Settings {
     region: Region,
     bucket: Option<String>,

net/aws/src/s3src/imp.rs

@@ -30,8 +30,10 @@ const DEFAULT_RETRY_ATTEMPTS: u32 = 5;
 const DEFAULT_REQUEST_TIMEOUT_MSEC: u64 = 15000;
 const DEFAULT_RETRY_DURATION_MSEC: u64 = 60_000;
 
+#[derive(Default)]
 #[allow(clippy::large_enum_variant)]
 enum StreamingState {
+    #[default]
     Stopped,
     Started {
         url: GstS3Url,
@@ -40,12 +42,6 @@ enum StreamingState {
     },
 }
 
-impl Default for StreamingState {
-    fn default() -> StreamingState {
-        StreamingState::Stopped
-    }
-}
-
 struct Settings {
     url: Option<GstS3Url>,
     access_key: Option<String>,

net/reqwest/src/reqwesthttpsrc/imp.rs

@@ -123,8 +123,9 @@ struct ClientContextInner {
 }
 
 #[allow(clippy::large_enum_variant)]
-#[derive(Debug)]
+#[derive(Debug, Default)]
 enum State {
+    #[default]
     Stopped,
     Started {
         uri: Url,
@@ -138,12 +139,6 @@ enum State {
     },
 }
 
-impl Default for State {
-    fn default() -> Self {
-        State::Stopped
-    }
-}
-
 #[derive(Debug, Default)]
 pub struct ReqwestHttpSrc {
     client: Mutex<Option<ClientContext>>,

video/ffv1/src/ffv1dec/imp.rs

@@ -21,7 +21,9 @@ use gst_video::VideoFormat;
 use once_cell::sync::Lazy;
 use std::sync::Mutex;
 
+#[derive(Default)]
 enum DecoderState {
+    #[default]
     Stopped,
     Started {
         output_info: Option<gst_video::VideoInfo>,
@@ -30,12 +32,6 @@ enum DecoderState {
     },
 }
 
-impl Default for DecoderState {
-    fn default() -> Self {
-        DecoderState::Stopped
-    }
-}
-
 #[derive(Default)]
 pub struct Ffv1Dec {
     state: Mutex<DecoderState>,