Move the CreateResult enum into the releases mod

This thing only needs to exist so Serde can decode the response JSON
properly. I'll either get a success, a missing token, *no body at all
which doesnt' make sense*, or some other ApiError text. In all cases,
the crate::Result is returned. This thing doesn't need to be public.

src/lib.rs

@@ -27,10 +27,3 @@ impl From<reqwest::Error> for crate::Error {
 
 type Result<T> = core::result::Result<T, Error>;
 
-#[derive(Debug, Deserialize, Serialize)]
-#[serde(untagged)]
-pub enum CreateResult {
-    Success(structs::release::Release),
-    ErrWithMessage(ApiError),
-    Empty,
-}