Fix deprecated use of extern crate

Author: mlafeldt

crates/duckdb/examples/appender.rs

@@ -1,5 +1,3 @@
-extern crate duckdb;
-
 use duckdb::{params, Connection, DropBehavior, Result};
 
 fn main() -> Result<()> {

crates/duckdb/examples/basic.rs

@@ -1,7 +1,5 @@
 // Basic example copy from README
 
-extern crate duckdb;
-
 use duckdb::{
     arrow::{record_batch::RecordBatch, util::pretty::print_batches},
     params, Connection, Result,

crates/duckdb/examples/hello-ext-capi/main.rs

@@ -1,7 +1,3 @@
-extern crate duckdb;
-extern crate duckdb_loadable_macros;
-extern crate libduckdb_sys;
-
 use duckdb::{
     core::{DataChunkHandle, Inserter, LogicalTypeHandle, LogicalTypeId},
     vtab::{BindInfo, InitInfo, TableFunctionInfo, VTab},

crates/duckdb/examples/hello-ext/main.rs

@@ -1,9 +1,5 @@
 #![warn(unsafe_op_in_unsafe_fn)]
 
-extern crate duckdb;
-extern crate duckdb_loadable_macros;
-extern crate libduckdb_sys;
-
 use duckdb::{
     core::{DataChunkHandle, Inserter, LogicalTypeHandle, LogicalTypeId},
     vtab::{BindInfo, InitInfo, TableFunctionInfo, VTab},

crates/duckdb/examples/parquet.rs

@@ -1,4 +1,3 @@
-extern crate duckdb;
 use duckdb::{
     arrow::{record_batch::RecordBatch, util::pretty::print_batches},
     Connection, Result,

crates/duckdb/src/r2d2.rs

@@ -125,7 +125,6 @@ impl r2d2::ManageConnection for DuckdbConnectionManager {
 
 #[cfg(test)]
 mod test {
-    extern crate r2d2;
     use super::*;
     use crate::types::Value;
     use std::{sync::mpsc, thread};

crates/duckdb/src/types/from_sql.rs

@@ -1,7 +1,8 @@
-extern crate cast;
+use std::{error::Error, fmt};
+
+use cast;
 
 use super::{TimeUnit, Value, ValueRef};
-use std::{error::Error, fmt};
 
 /// Enum listing possible errors from [`FromSql`] trait.
 #[derive(Debug)]