Remove the last traces of beaker.

There were still some traces of beaker around:
- docs: replaced by reference to itsdangerous.
- paste configs: Wiped away.
- config_spec.ini: wiped.
- test_mgoblin_app.ini: also wiped.

paste.ini

@@ -17,7 +17,6 @@ use = egg:Paste#urlmap
 
 [app:mediagoblin]
 use = egg:mediagoblin#app
-# filter-with = beaker
 config = %(here)s/mediagoblin_local.ini %(here)s/mediagoblin.ini
 
 [loggers]
@@ -57,14 +56,6 @@ use = egg:Paste#static
 document_root = %(here)s/user_dev/theme_static/
 cache_max_age = 86400
 
-[filter:beaker]
-use = egg:Beaker#beaker_session
-cache_dir = %(here)s/user_dev/beaker
-beaker.session.key = mediagoblin
-# beaker.session.secret = somesupersecret
-beaker.session.data_dir = %(here)s/user_dev/beaker/sessions/data
-beaker.session.lock_dir = %(here)s/user_dev/beaker/sessions/lock
-
 [filter:errors]
 use = egg:mediagoblin#errors
 debug = false