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/heltec_t114/T114Board.h

@@ -9,8 +9,9 @@
 #define  PIN_BAT_CTL      6
 #define  MV_LSB   (3000.0F / 4096.0F) // 12-bit ADC with 3.0V input range
 
-class T114Board : public NRF52Board {
+class T114Board : public NRF52BoardOTA {
 public:
+    T114Board() : NRF52BoardOTA("T114_OTA") {}
   void begin();
 
 #if defined(P_LORA_TX_LED)
@@ -50,6 +51,4 @@ public:
     #endif
     sd_power_system_off();
   }
-
-  bool startOTAUpdate(const char* id, char reply[]) override;
 };