MMU: Disable E-motor after Try-load-unload

The filament is never in the nozzle at this point so there
should be no oozing.

When a single material MMU print, I can hear audible noise
from the motor after executing Tx code. After some timeout
(while the heaters still heating up) I can hear the firmware
disable the E-motor. But we can safely disable it immediately
after the try-load-unload sequence.

Change in memory:
Flash: +4 bytes
SRAM: 0 bytes

Firmware/mmu2.cpp

@@ -304,6 +304,8 @@ bool MMU2::VerifyFilamentEnteredPTFE() {
         }
     }
 
+    Disable_E0();
+
     if (fsensorState) {
         IncrementLoadFails();
         return false;