fix: Get rid of some unnecessary trait bounds

Note: It's often tempting to put trait bounds on structs but in most
scenarios the general rule of thumb should be to use trait bounds
in impl blocks but let structs just declare data structures and
not behavior.

For further reading: https://stackoverflow.com/questions/49229332/should-trait-bounds-be-duplicated-in-struct-and-impl

libsigner/src/runloop.rs

@@ -93,12 +93,7 @@ pub trait SignerRunLoop<R: Send, CMD: Send> {
 }
 
 /// The top-level signer implementation
-pub struct Signer<
-    CMD: Send,
-    R: Send,
-    SL: SignerRunLoop<R, CMD> + Send + Sync,
-    EV: EventReceiver + Send,
-> {
+pub struct Signer<CMD, R, SL, EV> {
     /// the runloop itself
     signer_loop: Option<SL>,
     /// the event receiver to use
@@ -107,8 +102,6 @@ pub struct Signer<
     command_receiver: Option<Receiver<CMD>>,
     /// the result sender to use
     result_sender: Option<Sender<R>>,
-    /// marker to permit the R type
-    _phantom: PhantomData<R>,
 }
 
 /// The running signer implementation
@@ -215,7 +208,6 @@ impl<
             event_receiver: Some(event_receiver),
             command_receiver: Some(command_receiver),
             result_sender: Some(result_sender),
-            _phantom: PhantomData,
         }
     }