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_mesh_solar/MeshSolarBoard.h

@@ -20,9 +20,9 @@
 #define SX126X_DIO2_AS_RF_SWITCH  true
 #define SX126X_DIO3_TCXO_VOLTAGE   1.8
 
-
-class MeshSolarBoard : public NRF52Board {
+class MeshSolarBoard : public NRF52BoardOTA {
 public:
+  MeshSolarBoard() : NRF52BoardOTA("MESH_SOLAR_OTA") {}
   void begin();
 
   uint16_t getBattMilliVolts() override {
@@ -32,6 +32,4 @@ public:
   const char* getManufacturerName() const override {
     return "Heltec Mesh Solar";
   }
-
-  bool startOTAUpdate(const char* id, char reply[]) override;
 };