🧑‍💻 Simplify BIGTREE_SKR_2_F429 env

ini/stm32f4.ini

 # Bigtreetech SKR V2.0 F429 (STM32F429VGT6 ARM Cortex-M4) with USB Flash Drive Support
 #
 [env:BIGTREE_SKR_2_F429]
-extends                     = stm32_variant
-platform_packages           = ${stm_flash_drive.platform_packages}
+extends                     = env:BIGTREE_SKR_2
 board                       = marlin_STM32F429VGT6
-board_build.variant         = MARLIN_F4x7Vx
-board_build.offset          = 0x8000
-board_upload.offset_address = 0x08008000
-build_flags                 = ${stm_flash_drive.build_flags}
-                              -DUSE_USBHOST_HS -DUSE_USB_HS_IN_FS
-                              -DUSBD_IRQ_PRIO=5 -DUSBD_IRQ_SUBPRIO=6
-                              -DHSE_VALUE=8000000U -DHAL_SD_MODULE_ENABLED
-                              -DPIN_SERIAL3_RX=PD_9 -DPIN_SERIAL3_TX=PD_8
-upload_protocol             = stlink
 
 #
 # BigTreeTech SKR V2.0 F429 (STM32F429VGT6 ARM Cortex-M4) with USB Media Share Support