fix: Remove obsolete started parameter in UploadRequest (#673)

Author: PavlosTze

uploadservice/src/main/java/net/gotev/uploadservice/UploadRequest.kt

@@ -29,7 +29,6 @@ abstract class UploadRequest<B : UploadRequest<B>>
 constructor(protected val context: Context, protected var serverUrl: String) : Persistable {
 
     private var uploadId = UUID.randomUUID().toString()
-    private var started: Boolean = false
     protected var maxRetries = UploadServiceConfig.retryPolicy.defaultMaxRetries
     protected var autoDeleteSuccessfullyUploadedFiles = false
     protected var notificationConfig: (context: Context, uploadId: String) -> UploadNotificationConfig =
@@ -65,18 +64,11 @@ constructor(protected val context: Context, protected var serverUrl: String) : P
      * generated uploadId
      */
     open fun startUpload(): String {
-        check(!started) {
-            "You have already called startUpload() on this Upload request instance once and you " +
-                "cannot call it multiple times. Check your code."
-        }
-
         check(!UploadService.taskList.contains(uploadTaskParameters.id)) {
             "You have tried to perform startUpload() using the same uploadID of an " +
                 "already running task. You're trying to use the same ID for multiple uploads."
         }
 
-        started = true
-
         return context.startNewUpload(
             params = uploadTaskParameters,
             notificationConfig = notificationConfig(context, uploadId)