Merge rust-bitcoin/rust-secp256k1#664: Fix unit test import statements

dd6bf7c10d Fix unit test import statements (Tobin C. Harding)

Pull request description:

  In `lib.rs` unit tests we are getting build warnings because of how we are importing things, just import with `super::*` unconditionally and be done with it.

  This patch is the only good one out of #661.

ACKs for top commit:
  apoelstra:
    ACK dd6bf7c10d
  Kixunil:
    ACK dd6bf7c10d

Tree-SHA512: 3970f4c1374ec6de4798bfb52b561e9ac4611ec3a3885edc79639566f777e1fbb502cb36fa7abd015f3fd4a9ca4b6a4931b4ecb2e629e967b4e49391db97a97f

src/lib.rs

@@ -546,11 +546,7 @@ mod tests {
     #[cfg(target_arch = "wasm32")]
     use wasm_bindgen_test::wasm_bindgen_test as test;
 
-    #[allow(unused_imports)] // When building with no default features.
     use super::*;
-    use crate::{constants, ecdsa, from_hex, Error, Message};
-    #[cfg(feature = "alloc")]
-    use crate::{ffi, PublicKey, Secp256k1, SecretKey};
 
     macro_rules! hex {
         ($hex:expr) => {{