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/mesh_pocket/MeshPocket.h

@@ -9,9 +9,9 @@
 #define  PIN_BAT_CTL      34
 #define  MV_LSB   (3000.0F / 4096.0F) // 12-bit ADC with 3.0V input range
 
-class HeltecMeshPocket : public NRF52BoardDCDC, public NRF52BoardOTA {
+class HeltecMeshPocket : public NRF52BoardDCDC {
 public:
-  HeltecMeshPocket() : NRF52BoardOTA("MESH_POCKET_OTA") {}
+  HeltecMeshPocket() : NRF52Board("MESH_POCKET_OTA") {}
   void begin();
 
   uint16_t getBattMilliVolts() override {