Remove as_inner

`self` and the referenced type returned by `as_inner` are both `Copy`
types. There is no need to provide an reference getter method to a
`Copy` type since implementing `Copy` implies that copying is cheap.

src/util/address.rs

@@ -473,7 +473,7 @@ impl Payload {
     pub fn p2tr_tweaked(output_key: TweakedPublicKey) -> Payload {
         Payload::WitnessProgram {
             version: WitnessVersion::V1,
-            program: output_key.as_inner().serialize().to_vec(),
+            program: output_key.to_inner().serialize().to_vec(),
         }
     }
 

src/util/schnorr.rs

@@ -165,11 +165,6 @@ impl TweakedPublicKey {
         self.0
     }
 
-    /// Returns a reference to underlying public key.
-    pub fn as_inner(&self) -> &crate::XOnlyPublicKey {
-        &self.0
-    }
-
     /// Serialize the key as a byte-encoded pair of values. In compressed form
     /// the y-coordinate is represented by only a single bit, as x determines
     /// it up to one bit.