More flexibility to keep/remove R.class in static Java library

- Usually you don't need to set LOCAL_JAR_EXCLUDE_FILES in your
  Android.mk, if your static library is directly used by an app.
- If your library will be included by another library that need
  reference the R/Manifest class, you can set
  LOCAL_JAR_EXCLUDE_FILES := none
  to keep the generated classes.
- If your library includes another static library that has Android
  resource and you want to remove the generated classes carried by
  the static library, set:
  LOCAL_JAR_EXCLUDE_FILES := $(ANDROID_RESOURCE_GENERATED_CLASSES)

With the LOCAL_JAR_EXCLUDE_FILES value "none", deprecate the old
long variable LOCAL_KEEP_R_CLASS_IN_STATIC_JAVA_LIBRARY.

Change-Id: I3b9ad5d66f0262f784feb09bc1537c5b01256258