Disable DUAL_X_CARRIAGE by default

Marlin/Configuration_adv.h

@@ -150,7 +150,7 @@
 // A dual x-carriage design has the advantage that the inactive extruder can be parked which
 // prevents hot-end ooze contaminating the print. It also reduces the weight of each x-carriage
 // allowing faster printing speeds.
-#define DUAL_X_CARRIAGE
+//#define DUAL_X_CARRIAGE
 #ifdef DUAL_X_CARRIAGE
 // Configuration for second X-carriage
 // Note: the first x-carriage is defined as the x-carriage which homes to the minimum endstop;