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/ikoka_nano_nrf/IkokaNanoNRFBoard.h

@@ -6,8 +6,9 @@
 
 #ifdef XIAO_NRF52
 
-class IkokaNanoNRFBoard : public NRF52Board {
+class IkokaNanoNRFBoard : public NRF52BoardOTA {
 public:
+  IkokaNanoNRFBoard() : NRF52BoardOTA("XIAO_NRF52_OTA") {}
   void begin();
 
 #if defined(P_LORA_TX_LED)
@@ -46,8 +47,6 @@ public:
   const char *getManufacturerName() const override {
     return MANUFACTURER_STRING;
   }
-
-  bool startOTAUpdate(const char *id, char reply[]) override;
 };
 
 #endif