Remove unnecessary ? operator

clippy emits:

  warning: question mark operator is useless here

As suggested, remove the `?` operator.

Author: tcharding

src/util/amount.rs

@@ -1310,7 +1310,7 @@ pub mod serde {
         }
         fn des_btc<'d, D: Deserializer<'d>>(d: D) -> Result<Self, D::Error> {
             use serde::de::Error;
-            Ok(Amount::from_btc(f64::deserialize(d)?).map_err(D::Error::custom)?)
+            Amount::from_btc(f64::deserialize(d)?).map_err(D::Error::custom)
         }
     }
 
@@ -1338,7 +1338,7 @@ pub mod serde {
         }
         fn des_btc<'d, D: Deserializer<'d>>(d: D) -> Result<Self, D::Error> {
             use serde::de::Error;
-            Ok(SignedAmount::from_btc(f64::deserialize(d)?).map_err(D::Error::custom)?)
+            SignedAmount::from_btc(f64::deserialize(d)?).map_err(D::Error::custom)
         }
     }
 

src/util/psbt/mod.rs

@@ -269,7 +269,7 @@ mod display_from_str {
 
         fn from_str(s: &str) -> Result<Self, Self::Err> {
             let data = ::base64::decode(s).map_err(PsbtParseError::Base64Encoding)?;
-            Ok(encode::deserialize(&data).map_err(PsbtParseError::PsbtEncoding)?)
+            encode::deserialize(&data).map_err(PsbtParseError::PsbtEncoding)
         }
     }
 }