Remove unused key from StorageObject

Sources/Cache/MemoryStorage.swift

@@ -128,9 +128,9 @@ public enum MemoryStorage {
             
             let object: StorageObject<T>
             if config.keepWhenEnteringBackground {
-                object = BackgroundKeepingStorageObject(value, key: key, expiration: expiration)
+                object = BackgroundKeepingStorageObject(value, expiration: expiration)
             } else {
-                object = StorageObject(value, key: key, expiration: expiration)
+                object = StorageObject(value, expiration: expiration)
             }
             storage.setObject(object, forKey: key as NSString, cost: value.cacheCost)
             keys.insert(key)
@@ -255,13 +255,11 @@ extension MemoryStorage {
     class StorageObject<T> {
         var value: T?
         let expiration: StorageExpiration
-        let key: String
         
         private(set) var estimatedExpiration: Date
         
-        init(_ value: T, key: String, expiration: StorageExpiration) {
+        init(_ value: T, expiration: StorageExpiration) {
             self.value = value
-            self.key = key
             self.expiration = expiration
             
             self.estimatedExpiration = expiration.estimatedExpirationSinceNow

Tests/KingfisherTests/MemoryStorageTests.swift

@@ -256,7 +256,7 @@ class MemoryStorageTests: XCTestCase {
 
     func testStorageObject() {
         let now = Date()
-        let obj = MemoryStorage.StorageObject(1, key: "1", expiration: .seconds(1))
+        let obj = MemoryStorage.StorageObject(1, expiration: .seconds(1))
         XCTAssertEqual(obj.value, 1)
 
         XCTAssertEqual(