Do not dexpreopt system server jars from updatable modules.

Test: m

Test: The list of updatable system server jars is empty now,
  so I tested that the filer works with a manual experiment:
  - temporarily add wifi-service to PRODUCT_UPDATABLE_SYSTEM_SERVER_JARS
  - m nothing
  - fgrep -e 'wifi-service dexpreopt' $ANDROID_BUILD_TOP/out/build-$TARGET_PRODUCT.ninja
  - expect empty output (no dexpreopt command is generated)

Change-Id: Ia4206ccc263b535b6e39b54c6e8db28845ff2bf5