Revert "Merge pull request #108 from nox/store-clone"

This reverts commit 1c1af4b38b, reversing
changes made to da32be1fa9.

SslContextBuilder::cert_store_mut returns a &mut X509StoreBuilder
backed by a X509Store that is already shared with an existing SslContext.

boring/src/x509/store.rs

@@ -109,21 +109,4 @@ impl X509StoreRef {
     }
 }
 
-impl ToOwned for X509StoreRef {
-    type Owned = X509Store;
-
-    fn to_owned(&self) -> X509Store {
-        unsafe {
-            ffi::X509_STORE_up_ref(self.as_ptr());
-            X509Store::from_ptr(self.as_ptr())
-        }
-    }
-}
-
-impl Clone for X509Store {
-    fn clone(&self) -> Self {
-        (**self).to_owned()
-    }
-}
-
 use crate::ffi::X509_STORE_get0_objects;