[NO-JIRA]: [Rust] Revert a temporary workaround for a problem in Darl…

…ing dependency

Introduced-with: 2c484c6
Fixed upstream with: TedDriggs/darling#296

Signed-off-by: Martin Tzvetanov Grigorov <mgrigorov@apache.org>

lang/rust/avro_derive/src/lib.rs

@@ -15,10 +15,6 @@
 // specific language governing permissions and limitations
 // under the License.
 
-// for Rust versions older than 1.79.0
-#![allow(unknown_lints)]
-// Allow until https://github.com/TedDriggs/darling/pull/292 is resolved
-#![allow(clippy::manual_unwrap_or_default)]
 use darling::FromAttributes;
 use proc_macro2::{Span, TokenStream};
 use quote::quote;