Remove unnecessary explicit type annotation

The compiler can infer this type, no need for an explicit type
annotation.

src/util/key.rs

@@ -183,7 +183,7 @@ impl PublicKey {
 
     /// Deserialize a public key from a slice
     pub fn from_slice(data: &[u8]) -> Result<PublicKey, Error> {
-        let compressed: bool = match data.len() {
+        let compressed = match data.len() {
             33 => true,
             65 => false,
             len =>  {