Avoid redudant imports

`cargo check` of nightly flags it, which is used for testing in
`libz-sys`.

src/ffi/c.rs

@@ -8,7 +8,7 @@ use std::os::raw::{c_int, c_uint, c_void};
 use std::ptr;
 
 use super::*;
-use crate::mem::{self, FlushDecompress, Status};
+use crate::mem;
 
 #[derive(Default)]
 pub struct ErrorMessage(Option<&'static str>);
@@ -127,6 +127,7 @@ extern "C" fn zfree(_ptr: *mut c_void, address: *mut c_void) {
 }
 
 unsafe impl<D: Direction> Send for Stream<D> {}
+
 unsafe impl<D: Direction> Sync for Stream<D> {}
 
 /// Trait used to call the right destroy/end function on the inner
@@ -137,6 +138,7 @@ pub trait Direction {
 
 #[derive(Debug)]
 pub enum DirCompress {}
+
 #[derive(Debug)]
 pub enum DirDecompress {}
 
@@ -176,6 +178,7 @@ impl Direction for DirCompress {
         mz_deflateEnd(stream)
     }
 }
+
 impl Direction for DirDecompress {
     unsafe fn destroy(stream: *mut mz_stream) -> c_int {
         mz_inflateEnd(stream)
@@ -410,6 +413,7 @@ mod c_backend {
     pub use libz::Z_STREAM_END as MZ_STREAM_END;
     pub use libz::Z_STREAM_ERROR as MZ_STREAM_ERROR;
     pub use libz::Z_SYNC_FLUSH as MZ_SYNC_FLUSH;
+
     pub type AllocSize = libz::uInt;
 
     pub const MZ_DEFAULT_WINDOW_BITS: c_int = 15;
@@ -438,6 +442,7 @@ mod c_backend {
             mem::size_of::<mz_stream>() as c_int,
         )
     }
+
     pub unsafe extern "C" fn mz_inflateInit2(stream: *mut mz_stream, window_bits: c_int) -> c_int {
         libz::inflateInit2_(
             stream,