Deduplicate NRF52 startOTAUpdate()

The startOTAUpdate() is the same for all NRF52 boards. Use a common
implementation for all boards that currently have a specific
implementation.

The following boards currently have an empty startOTAUpdate() for
whatever reasons and therefore are not inheriting NRF52BoardOTA to
keep the same state: Nano G2 Ultra, Seeed SenseCAP T1000-E,
Wio WM1110.

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

variants/thinknode_m1/ThinkNodeM1Board.h

@@ -13,12 +13,11 @@
 #define PIN_VBAT_READ     (4)
 #define REAL_VBAT_MV_PER_LSB (VBAT_DIVIDER_COMP * VBAT_MV_PER_LSB)
 
-class ThinkNodeM1Board : public NRF52Board {
+class ThinkNodeM1Board : public NRF52BoardOTA {
 public:
-
+  ThinkNodeM1Board() : NRF52BoardOTA("THINKNODE_M1_OTA") {}
   void begin();
   uint16_t getBattMilliVolts() override;
-  bool startOTAUpdate(const char* id, char reply[]) override;
 
   #if defined(P_LORA_TX_LED)
   void onBeforeTransmit() override {