bsd dd: include prebuilt bsd dd in twrp for Nougat and greater

- Cleaned up toolbox/Android.mk so that BSD dd builds
  with correct Android versions

Change-Id: Idb15811480ec03b05336d54b866233b5ac99dfaf
diff --git a/toybox/Android.mk b/toybox/Android.mk
index c21a272..5f6edec 100644
--- a/toybox/Android.mk
+++ b/toybox/Android.mk
@@ -485,7 +485,6 @@
     arp \
     base64 \
     chattr \
-    dd \
     df \
     diff \
     flock \
@@ -547,7 +546,7 @@
     gzip \
     gunzip \
     zcat
-ifeq ($(shell test $(PLATFORM_SDK_VERSION) -gt 27; echo $$?),0)
+ifeq ($(shell test $(PLATFORM_SDK_VERSION) -gt 25; echo $$?),0)
 ALL_TOOLS += \
     fmt \
     start \