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/keepteen_lt1/KeepteenLT1Board.h

@@ -4,11 +4,12 @@
 #include <Arduino.h>
 #include <helpers/NRF52Board.h>
 
-class KeepteenLT1Board : public NRF52Board {
+class KeepteenLT1Board : public NRF52BoardOTA {
 protected:
   uint8_t btn_prev_state;
 
 public:
+  KeepteenLT1Board() : NRF52BoardOTA("KeepteenLT1_OTA") {}
   void begin();
 
   #define BATTERY_SAMPLES 8
@@ -40,6 +41,4 @@ public:
   void powerOff() override {
     sd_power_system_off();
   }
-
-  bool startOTAUpdate(const char* id, char reply[]) override;
 };