Drop the "max previewable file size" limit

which was originally introduced to work around timing issues causing
us to try (and fail) to generate previews on sqlite read replicas.

lib/rails_ext/active_storage_blob_previewable.rb

@@ -1,18 +0,0 @@
-#
-#  see https://app.fizzy.do/5986089/collections/7/cards/1302
-#
-#  Large previewable uploads may take longer than the "pin reads" interval. So we pick a small-ish
-#  number and turn off previews for anything larger, at least until we can come up with a permanent
-#  solution.
-#
-module ActiveStorageBlobPreviewable
-  MAX_PREVIEWABLE_SIZE = 16.megabytes # this is pretty arbitrary, feel free to adjust
-
-  def previewable?
-    super && self.byte_size <= MAX_PREVIEWABLE_SIZE
-  end
-end
-
-ActiveSupport.on_load :active_storage_blob do
-  prepend ::ActiveStorageBlobPreviewable
-end