Clean up W25QXXFlash class

Marlin/src/gcode/control/M993_M994.cpp

     return;
   }
 
-  W25QXXFlash W25QXX;
-
   uint8_t buf[1024];
   uint32_t addr = 0;
   W25QXX.init(SPI_QUARTER_SPEED);
     return;
   }
 
-  W25QXXFlash W25QXX;
-
   uint8_t buf[1024];
   uint32_t addr = 0;
   W25QXX.init(SPI_QUARTER_SPEED);

Marlin/src/lcd/extui/lib/mks_ui/SPIFlashStorage.cpp

 #include "../../../../inc/MarlinConfig.h"
 #include "SPIFlashStorage.h"
 
-extern W25QXXFlash W25QXX;
-
 uint8_t SPIFlashStorage::m_pageData[SPI_FLASH_PageSize];
 uint32_t SPIFlashStorage::m_currentPage;
 uint16_t SPIFlashStorage::m_pageDataUsed;

Marlin/src/lcd/extui/lib/mks_ui/draw_ui.cpp

   #include "../../../../feature/pause.h"
 #endif
 
-W25QXXFlash W25QXX;
 CFG_ITMES gCfgItems;
 UI_CFG uiCfg;
 DISP_STATE_STACK disp_state_stack;

Marlin/src/lcd/extui/lib/mks_ui/pic_manager.h

 extern void default_view_Read(uint8_t *default_view_Rbuff, uint32_t default_view_Readsize);
 extern void flash_view_Read(uint8_t *flash_view_Rbuff, uint32_t flash_view_Readsize);
 
-extern W25QXXFlash W25QXX;
-
 #ifdef __cplusplus
 } /* C-declarations for C++ */
 #endif

Marlin/src/libs/W25Qxx.cpp

 
 #if HAS_SPI_FLASH
 
+#include "W25Qxx.h"
 #include <SPI.h>
 
-#include "W25Qxx.h"
+W25QXXFlash W25QXX;
 
 #ifndef SPI_FLASH_MISO_PIN
   #define SPI_FLASH_MISO_PIN W25QXX_MISO_PIN

Marlin/src/libs/W25Qxx.h

-/**
+/**
  * Marlin 3D Printer Firmware
  * Copyright (c) 2020 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
  *
  */
 #pragma once
 
-//#ifdef __cplusplus
-//extern "C" { /* C-declarations for C++ */
-//#endif
-
 #include <stdint.h>
 
 #define W25X_WriteEnable        0x06
   static void SPI_FLASH_BufferRead(uint8_t* pBuffer, uint32_t ReadAddr, uint16_t NumByteToRead);
 };
 
-//#ifdef __cplusplus
-//} /* C-declarations for C++ */
-//#endif
+extern W25QXXFlash W25QXX;