Cleanups for unbundling

* android.security is hidden.  Use java.security.MessageDigest instead.
* Remove android-common from makefile (we no longer use it)
* Add LOCAL_SDK_VERSION to makefile and comment it out

Change-Id: I7f9a021387d5c4e47ade1adb0bb75bec82ba0dd8
diff --git a/Android.mk b/Android.mk
index da7fc5c..5707fe2 100644
--- a/Android.mk
+++ b/Android.mk
@@ -24,7 +24,8 @@
     src/com/android/email/service/IEmailServiceCallback.aidl
 # EXCHANGE-REMOVE-SECTION-END
 
-LOCAL_STATIC_JAVA_LIBRARIES := android-common
+# Revive this when the app is unbundled.
+# LOCAL_SDK_VERSION := current
 
 LOCAL_PACKAGE_NAME := Email