Remove virtual from interface operator definitions

drivers/include/drivers/interfaces/InterfaceDigitalIn.h

@@ -38,7 +38,7 @@ struct DigitalIn {
     virtual void mode(PinMode pull) = 0;
     virtual int is_connected() = 0;
 
-    virtual operator int()
+    operator int()
     {
         // Underlying implementation is responsible for thread-safety
         return read();

drivers/include/drivers/interfaces/InterfaceDigitalInOut.h

@@ -42,21 +42,21 @@ struct DigitalInOut {
     virtual void mode(PinMode pull) = 0;
     virtual int is_connected() = 0;
 
-    virtual DigitalInOut &operator= (int value)
+    DigitalInOut &operator= (int value)
     {
         // Underlying implementation is responsible for thread-safety
         write(value);
         return *this;
     }
 
-    virtual DigitalInOut &operator= (DigitalInOut &rhs)
+    DigitalInOut &operator= (DigitalInOut &rhs)
     {
         // Underlying implementation is responsible for thread-safety
         write(rhs.read());
         return *this;
     }
 
-    virtual operator int()
+    operator int()
     {
         // Underlying implementation is responsible for thread-safety
         return read();

drivers/include/drivers/interfaces/InterfaceDigitalOut.h

@@ -39,21 +39,21 @@ struct DigitalOut {
     virtual int read() = 0;
     virtual int is_connected() = 0;
 
-    virtual DigitalOut &operator= (int value)
+    DigitalOut &operator= (int value)
     {
         // Underlying implementation is responsible for thread-safety
         write(value);
         return *this;
     }
 
-    virtual DigitalOut &operator= (DigitalOut &rhs)
+    DigitalOut &operator= (DigitalOut &rhs)
     {
         // Underlying implementation is responsible for thread-safety
         write(rhs.read());
         return *this;
     }
 
-    virtual operator int()
+    operator int()
     {
         // Underlying implementation is responsible for thread-safety
         return read();