🔨 Remove obsolete ON_BOARD_SPI_DEVICE

Marlin/src/pins/lpc1769/pins_BTT_SKR_E3_TURBO.h

 #elif SD_CONNECTION_IS(CUSTOM_CABLE)
   #error "SD CUSTOM_CABLE is not compatible with SKR E3 Turbo."
 #endif
-
-#define ON_BOARD_SPI_DEVICE                    1  // SPI1

Marlin/src/pins/stm32f1/pins_BTT_SKR_CR6.h

 
 #if SD_CONNECTION_IS(ONBOARD)
   #define SD_DETECT_PIN                     PC4
-
-  #define ON_BOARD_SPI_DEVICE                  1  // SPI1
   #define ONBOARD_SD_CS_PIN                 PA4   // Chip select for "System" SD card
 #endif