Fix clippy warnings

src/vtab/array.rs

@@ -26,7 +26,6 @@
 //! }
 //! ```
 
-use std::default::Default;
 use std::marker::PhantomData;
 use std::os::raw::{c_char, c_int, c_void};
 use std::rc::Rc;

src/vtab/mod.rs

@@ -11,7 +11,6 @@
 //! (See [SQLite doc](http://sqlite.org/vtab.html))
 use std::borrow::Cow::{self, Borrowed, Owned};
 use std::marker::PhantomData;
-use std::marker::Sync;
 use std::os::raw::{c_char, c_int, c_void};
 use std::ptr;
 use std::slice;

src/vtab/series.rs

@@ -3,7 +3,6 @@
 //! Port of C [generate series
 //! "function"](http://www.sqlite.org/cgi/src/finfo?name=ext/misc/series.c):
 //! `https://www.sqlite.org/series.html`
-use std::default::Default;
 use std::marker::PhantomData;
 use std::os::raw::c_int;
 

src/vtab/vtablog.rs

@@ -1,5 +1,4 @@
 //! Port of C [vtablog](http://www.sqlite.org/cgi/src/finfo?name=ext/misc/vtablog.c)
-use std::default::Default;
 use std::marker::PhantomData;
 use std::os::raw::c_int;
 use std::str::FromStr;