Remove NRF52BoardOTA class and integrate it into NRF52Board

As all NRF52 boards now have OTA support, let's remove the subclass
and integrate it into the base class.

Signed-off-by: Frieder Schrempf <frieder@fris.de>

variants/keepteen_lt1/KeepteenLT1Board.h

@@ -4,12 +4,12 @@
 #include <Arduino.h>
 #include <helpers/NRF52Board.h>
 
-class KeepteenLT1Board : public NRF52BoardOTA {
+class KeepteenLT1Board : public NRF52Board {
 protected:
   uint8_t btn_prev_state;
 
 public:
-  KeepteenLT1Board() : NRF52BoardOTA("KeepteenLT1_OTA") {}
+  KeepteenLT1Board() : NRF52Board("KeepteenLT1_OTA") {}
   void begin();
 
   #define BATTERY_SAMPLES 8