Deduplicate reboot() for NRF52 boards

The reboot() method is the same for all NRF52 boards. Use a shared
implementation.

Signed-off-by: Frieder Schrempf <frieder@fris.de>

variants/minewsemi_me25ls01/MinewsemiME25LS01Board.h

@@ -80,10 +80,5 @@ public:
   }
 #endif
 
-
-  void reboot() override {
-    NVIC_SystemReset();
-  }
-
   bool startOTAUpdate(const char* id, char reply[]) override;
 };