Bug 1622111 - Convert security.data_uri.unique_opaque_origin to static pref and remove ClientPrefs. r=njn

Converts security.data_uri.unique_opaque_origin to a static pref. This pref was initialized by the ClientManager in ClientPrefs, so this commit also removes those files. Somehow this pref was getting added in VarCache twice, so it also removes the places where the pref was added in Networking.

Differential Revision: https://phabricator.services.mozilla.com/D67185

docshell/base/nsDocShell.cpp

@@ -37,6 +37,7 @@
 #include "mozilla/StaticPrefs_dom.h"
 #include "mozilla/StaticPrefs_extensions.h"
 #include "mozilla/StaticPrefs_privacy.h"
+#include "mozilla/StaticPrefs_security.h"
 #include "mozilla/StaticPrefs_ui.h"
 #include "mozilla/StaticPrefs_fission.h"
 #include "mozilla/StartupTimeline.h"
@@ -9860,8 +9861,9 @@ nsresult nsDocShell::DoURILoad(nsDocShellLoadState* aLoadState,
         true,  // aInheritForAboutBlank
         isSrcdoc);
 
-    bool isURIUniqueOrigin = nsIOService::IsDataURIUniqueOpaqueOrigin() &&
-                             SchemeIsData(aLoadState->URI());
+    bool isURIUniqueOrigin =
+        StaticPrefs::security_data_uri_unique_opaque_origin() &&
+        SchemeIsData(aLoadState->URI());
     inheritPrincipal = inheritAttrs && !isURIUniqueOrigin;
   }