Remove the file context rule for /system/bin/bspatch.

update_engine no longer needs a standalone bspatch executable since [1]
(which first landed into O). And we don't ship /system/bin/bspatch on
device by default.

[1] https://android-review.googlesource.com/c/platform/system/update_engine/+/327365

Test: Verify that /system/bin/bspatch doesn't exist on device.
Test: Trigger an A/B OTA install for aosp_walleye-userdebug:
      `m dist`;
      `system/update_engine/scripts/update_device.py out/dist/aosp_walleye-ota.zip`.
      No update_engine related denial.
Change-Id: Iff578bdb0b1909092dd19feff069755a44d29398