Bug 517478 - signon.expireMasterPassword is obsolete and should be removed; (Bv1-TK) Remove obsolete default pref value

r=dolske

modules/libpref/src/init/all.js

@@ -2728,7 +2728,6 @@ pref("print.print_command", "lp -c -s ${MOZ_PRINTER_NAME:+-d\"$MOZ_PRINTER_NAME\
 
 // Login Manager prefs
 pref("signon.rememberSignons",              true);
-pref("signon.expireMasterPassword",         false);
 pref("signon.SignonFileName",               "signons.txt"); // obsolete 
 pref("signon.SignonFileName2",              "signons2.txt"); // obsolete
 pref("signon.SignonFileName3",              "signons3.txt"); // obsolete