mpc83xx: mpc8349 - delete unused SYS_MID_FLASH_JUMP

This was introduced with the MPC8349EMDS board, and then copied to
a couple other boards by nature of being the reference implementation.

  u-boot$git grep CONFIG_SYS_MID_FLASH_JUMP
  include/configs/MPC8349EMDS.h:#define CONFIG_SYS_MID_FLASH_JUMP 0x7F000000
  include/configs/sbc8349.h:#define CONFIG_SYS_MID_FLASH_JUMP     0x7F000000
  include/configs/vme8349.h:#define CONFIG_SYS_MID_FLASH_JUMP     0x7F000000
  u-boot$

It currently isn't used, so delete it before it spreads further.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>