sepolicy : removed msm_fb_persist_mode secontext

As secontext for the following path has been moved to common
folder we are removing  defination from target related file_contexts
files  to avoid "Multiple same specifications " error during
compile time.
sys/devices/virtual/graphics/fb([0-3])+/msm_fb_persist_mode

Change-Id: Ifeeab19d79429e71057c4d7977386b0a33fad797