Bug 1407230 - Don't set devtools.debugger.client-source-maps-enabled pref; r=jdescottes

This removes the last spot that sets the obsolete
devtools.debugger.client-source-maps-enabled pref.  Note that the
definition of the pref remains; it will be deleted upstream once this
lands, and then removed from M-C by the next debugger bundle landing.

MozReview-Commit-ID: DTd2iDJI1y0

--HG--
extra : rebase_source : f7ac30f2ef707c11ad3d717ea49d13e1e883bd95

devtools/client/framework/toolbox-process-window.js

@@ -76,7 +76,6 @@ function setPrefDefaults() {
   // Bug 1225160 - Using source maps with browser debugging can lead to a crash
   Services.prefs.setBoolPref("devtools.debugger.source-maps-enabled", false);
   Services.prefs.setBoolPref("devtools.debugger.new-debugger-frontend", true);
-  Services.prefs.setBoolPref("devtools.debugger.client-source-maps-enabled", true);
   Services.prefs.setBoolPref("devtools.webconsole.new-frontend-enabled", false);
 }
 window.addEventListener("load", function () {