Bug 1835440 - Remove unused plugins.http_https_only pref r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D179287

modules/libpref/init/StaticPrefList.yaml

@@ -12888,15 +12888,6 @@
   value: true
   mirror: always
 
-#---------------------------------------------------------------------------
-# Prefs starting with "plugins."
-#---------------------------------------------------------------------------
-
-- name: plugins.http_https_only
-  type: bool
-  value: true
-  mirror: always
-
 #---------------------------------------------------------------------------
 # Prefs starting with "preferences."
 #---------------------------------------------------------------------------

modules/libpref/moz.build

@@ -72,7 +72,6 @@ pref_groups = [
     "permissions",
     "places",
     "plain_text",
-    "plugins",
     "preferences",
     "print",
     "privacy",