Remove unneeded unit return type

Clippy emits:

    warning: unneeded unit return type

As suggested, remove the unneeded unit return type

Author: tcharding

src/interpreter/mod.rs

@@ -565,7 +565,7 @@ where
         node: &'intp Miniscript<BitcoinKey, NoChecks>,
         n_evaluated: usize,
         n_satisfied: usize,
-    ) -> () {
+    ) {
         self.state.push(NodeEvaluationState {
             node,
             n_evaluated,

src/interpreter/stack.rs

@@ -115,7 +115,7 @@ impl<'txin> Stack<'txin> {
     }
 
     /// Pushes an element onto the top of the stack
-    pub fn push(&mut self, elem: Element<'txin>) -> () {
+    pub fn push(&mut self, elem: Element<'txin>) {
         self.0.push(elem);
     }