Bug 773460; backout the changes to b2g.js because they are unnecessary. r=cjones

--HG--
extra : rebase_source : 41844d8d001b22b285005dbc634c39ad9b61a9f6

b2g/app/b2g.js

@@ -142,10 +142,6 @@ pref("browser.xul.error_pages.enabled", true);
 // disable color management
 pref("gfx.color_management.mode", 0);
 
-//prefer Azure/Cairo canvas
-pref("gfx.canvas.azure.enabled", true);
-pref("gfx.canvas.azure.backends", "cairo");
-
 // don't allow JS to move and resize existing windows
 pref("dom.disable_window_move_resize", true);