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/lilygo_techo_lite/TechoBoard.h

@@ -13,11 +13,11 @@
 #define PIN_VBAT_READ     (4)
 #define REAL_VBAT_MV_PER_LSB (VBAT_DIVIDER_COMP * VBAT_MV_PER_LSB)
 
-class TechoBoard : public NRF52Board {
+class TechoBoard : public NRF52BoardOTA {
 public:
+  TechoBoard() : NRF52BoardOTA("TECHO_OTA") {}
   void begin();
   uint16_t getBattMilliVolts() override;
-  bool startOTAUpdate(const char* id, char reply[]) override;
 
   const char* getManufacturerName() const override {
     return "LilyGo T-Echo";