Use trim_start_matches

Now that we are bumping the MSRV to greater than 1.30 we can use
`trim_start_matches`.

Use `trim_start_matches` and remove the clippy directive.

Author: tcharding

src/util/psbt/map/input.rs

@@ -166,7 +166,6 @@ impl fmt::Display for PsbtSighashType {
     }
 }
 
-#[allow(deprecated)]  // TODO: Swap `trim_left_matches` for `trim_start_matches` once MSRV >= 1.30.
 impl FromStr for PsbtSighashType {
     type Err = SighashTypeParseError;
 
@@ -184,7 +183,7 @@ impl FromStr for PsbtSighashType {
         }
 
         // We accept non-standard sighash values.
-        if let Ok(inner) = u32::from_str_radix(s.trim_left_matches("0x"), 16) {
+        if let Ok(inner) = u32::from_str_radix(s.trim_start_matches("0x"), 16) {
             return Ok(PsbtSighashType { inner });
         }