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/xiao_nrf52/XiaoNrf52Board.h

@@ -6,8 +6,9 @@
 
 #ifdef XIAO_NRF52
 
-class XiaoNrf52Board : public NRF52BoardDCDC {
+class XiaoNrf52Board : public NRF52BoardDCDC, public NRF52BoardOTA {
 public:
+  XiaoNrf52Board() : NRF52BoardOTA("XIAO_NRF52_OTA") {}
   void begin();
 
 #if defined(P_LORA_TX_LED)
@@ -56,8 +57,6 @@ public:
 
     sd_power_system_off();
   }
-
-  bool startOTAUpdate(const char* id, char reply[]) override;
 };
 
 #endif