Download: Remove unnecessary unit test.

A unit test only for compiling MockDownloadItem is not needed.

Bug: NONE
Change-Id: I106c2a9a5bacad516373905df1d4e8141ff1c441
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2250930
Commit-Queue: Xing Liu <xingliu@chromium.org>
Reviewed-by: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#779558}

components/download/internal/common/download_item_impl_unittest.cc

@@ -30,7 +30,6 @@
 #include "components/download/public/common/download_item_impl_delegate.h"
 #include "components/download/public/common/download_url_parameters.h"
 #include "components/download/public/common/mock_download_file.h"
-#include "components/download/public/common/mock_download_item.h"
 #include "crypto/secure_hash.h"
 #include "net/http/http_response_headers.h"
 #include "testing/gmock/include/gmock/gmock.h"
@@ -2601,8 +2600,4 @@ TEST_P(DownloadItemDestinationUpdateRaceTest, IntermediateRenameSucceeds) {
   task_environment_.RunUntilIdle();
 }
 
-TEST(MockDownloadItem, Compiles) {
-  MockDownloadItem mock_item;
-}
-
 }  // namespace download