Drop BOARD_SEPOLICY_UNION.

As suggested in the comments on
https://android-review.googlesource.com/#/c/141560/
drop BOARD_SEPOLICY_UNION and simplify the build_policy logic.
Union all files found under BOARD_SEPOLICY_DIRS.

Change-Id: I4214893c999c23631f5456cb1b8edd59771ef13b
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>
diff --git a/BoardConfig.mk b/BoardConfig.mk
index e756002..dc25d68 100644
--- a/BoardConfig.mk
+++ b/BoardConfig.mk
@@ -36,14 +36,3 @@
 BOARD_FLASH_BLOCK_SIZE := 512
 TARGET_USERIMAGES_SPARSE_EXT_DISABLED := true
 BOARD_SEPOLICY_DIRS += build/target/board/generic/sepolicy
-BOARD_SEPOLICY_UNION += \
-        bootanim.te \
-        device.te \
-        domain.te \
-        file.te \
-        file_contexts \
-        qemud.te \
-        rild.te \
-        shell.te \
-        surfaceflinger.te \
-        system_server.te