Revert "Invoke mogrify once when transforming an image"

This reverts commit a80f81af.

activestorage/app/models/active_storage/variation.rb

@@ -44,15 +44,13 @@ def initialize(transformations)
   end
 
   # Accepts an open MiniMagick image instance, like what's returned by <tt>MiniMagick::Image.read(io)</tt>,
-  # and performs the +transformations+ against it.
+  # and performs the +transformations+ against it. The transformed image instance is then returned.
   def transform(image)
-    image.mogrify do |command|
-      transformations.each do |method, argument|
-        if eligible_argument?(argument)
-          command.public_send(method, argument)
-        else
-          command.public_send(method)
-        end
+    transformations.each do |(method, argument)|
+      if eligible_argument?(argument)
+        image.public_send(method, argument)
+      else
+        image.public_send(method)
       end
     end
   end