Revert "Convert some DCHECK to CHECK to find cases that download file is not"

This reverts commit bac094f7.

The CHECK captures the crash, no longer needed

Original change's description:
> Convert some DCHECK to CHECK to find cases that download file is not
> properly deleted
> 
> 
> BUG=1028666
> 
> Change-Id: I59b60a897a5f2529d4e61d8632aebe421dbc71b3
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1933738
> Reviewed-by: Xing Liu <xingliu@chromium.org>
> Commit-Queue: Min Qin <qinmin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#719294}

TBR=qinmin@chromium.org,xingliu@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: 1028666
Change-Id: Ia0cdac36ec67ad41a669b55bf32343a1dd18afba
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1946430Reviewed-by: Min Qin <qinmin@chromium.org>
Commit-Queue: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#720533}

components/download/internal/common/download_item_impl.cc

@@ -446,7 +446,7 @@ DownloadItemImpl::~DownloadItemImpl() {
 
   // Should always have been nuked before now, at worst in
   // DownloadManager shutdown.
-  CHECK(!download_file_);
+  DCHECK(!download_file_);
   CHECK(!is_updating_observers_);
 
   for (auto& observer : observers_)
@@ -1447,7 +1447,7 @@ void DownloadItemImpl::Start(
     URLLoaderFactoryProvider::URLLoaderFactoryProviderPtr
         url_loader_factory_provider) {
   DCHECK_CALLED_ON_VALID_THREAD(thread_checker_);
-  CHECK(!download_file_);
+  DCHECK(!download_file_);
   DVLOG(20) << __func__ << "() this=" << DebugString(true);
   RecordDownloadCountWithSource(START_COUNT, download_source_);