Fix issue attachment handling (#24202)

Close #24195

Some of the changes are taken from my another fix
https://github.com/go-gitea/gitea/pull/20147/commits/f07b0de997125c9b79cc5af27966a7cdd1803a4d
in #20147 (although that PR was discarded ....)


The bug is:

1. The old code doesn't handle `removedfile` event correctly
2. The old code doesn't provide attachments for type=CommentTypeReview


This PR doesn't intend to refactor the "upload" code to a perfect state
(to avoid making the review difficult), so some legacy styles are kept.

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: Giteabot <teabot@gitea.io>

web_src/css/features/dropzone.css

@@ -51,13 +51,3 @@
 .dropzone .dz-preview:hover .dz-image img {
   filter: opacity(0.5) !important;
 }
-
-.dropzone-attachments .divider {
-  margin-top: 0 !important;
-  margin-bottom: 0 !important;
-}
-
-.dropzone-attachments .grid,
-.dropzone-attachments .thumbnails {
-  padding: .5rem 1rem;
-}