uploads: disallow uploading new Flash files.

Flash is dead. It's no longer supported by browsers, it's not
well-supported by emulators, and only two Flash posts were uploaded in
the last year anyway. Old Flash files will continue to exist, but new
Flash uploads will no longer be allowed.

app/models/upload.rb

@@ -13,8 +13,8 @@ class Upload < ApplicationRecord
     end
 
     def validate_file_ext(record)
-      if record.file_ext == "bin"
-        record.errors.add(:file_ext, "is invalid (only JPEG, PNG, GIF, SWF, MP4, and WebM files are allowed")
+      if record.file_ext.in?(["bin", "swf"])
+        record.errors.add(:file_ext, "is invalid (only JPEG, PNG, GIF, MP4, and WebM files are allowed")
       end
     end
 

app/views/uploads/new.html.erb

@@ -31,7 +31,7 @@
 
         <div class="input" id="filedropzone">
           <div class="dropzone-hint">Click or drag and drop to upload a file</div>
-          <div class="dropzone-hint hint">Max size: <%= number_to_human_size(Danbooru.config.max_file_size) %>. Supported filetypes: jpg, png, gif, swf, mp4, webm.</div>
+          <div class="dropzone-hint hint">Max size: <%= number_to_human_size(Danbooru.config.max_file_size) %>. Supported filetypes: jpg, png, gif, mp4, webm.</div>
         </div>
 
         <div class="input string optional upload_source">

test/functional/uploads_controller_test.rb

@@ -287,7 +287,7 @@ class UploadsControllerTest < ActionDispatch::IntegrationTest
         should_upload_successfully("test/files/test-animated-86x52.gif")
         should_upload_successfully("test/files/test-300x300.mp4")
         should_upload_successfully("test/files/test-512x512.webm")
-        should_upload_successfully("test/files/compressed.swf")
+        # should_upload_successfully("test/files/compressed.swf")
       end
 
       context "uploading a file from a source" do