Remove unused headers (#4954)

These files had existing since 2020 without being used/modified.

src/platform/esp32/CallbackCharacteristic.h

@@ -1,12 +0,0 @@
-#pragma once
-#include "BLECharacteristic.h"
-#include "PowerFSM.h" // FIXME - someday I want to make this OTA thing a separate lb at at that point it can't touch this
-
-/**
- * A characteristic with a set of overridable callbacks
- */
-class CallbackCharacteristic : public BLECharacteristic, public BLECharacteristicCallbacks
-{
-  public:
-    CallbackCharacteristic(const char *uuid, uint32_t btprops) : BLECharacteristic(uuid, btprops) { setCallbacks(this); }
-};

src/platform/nrf52/pgmspace.h

@@ -1,5 +0,0 @@
-#pragma once
-
-// dummy file to keep old arduino code happy
-#define PROGMEM
-#define pgm_read_byte(addr) (*((unsigned const char *)addr))