Revert to using Paperclip's filesystem storage, and fix dangling records in remove_remote (#8339)

* Fix uncaching worker

* Revert to using Paperclip's filesystem backend instead of fog-local

fog-local has lots of concurrency issues, causing failure to delete files,
dangling file records, and spurious errors UncacheMediaWorker

Gemfile.lock

@@ -220,8 +220,6 @@ GEM
     fog-json (1.0.2)
       fog-core (~> 1.0)
       multi_json (~> 1.10)
-    fog-local (0.5.0)
-      fog-core (>= 1.27, < 3.0)
     fog-openstack (0.1.25)
       fog-core (~> 1.40)
       fog-json (>= 1.0)
@@ -679,7 +677,6 @@ DEPENDENCIES
   fast_blank (~> 1.0)
   fastimage
   fog-core (~> 1.45)
-  fog-local (~> 0.5)
   fog-openstack (~> 0.1)
   fuubar (~> 2.2)
   goldfinger (~> 2.1)