RRO shouldn't depend on frameworks or system(_ext) app when TARGET_BUILD_UNBUNDLED

In the case of unbundled build, the module in vendor should use
system(_ext) module by prebuilt one. But RRO depends on system module
directly depending on some conditions(packages exporting resources)

In this change,
 1. Temporarily make LOCAL_RES_LIBRARIES empty(For now, auto generated
 RRO doesn't use overlaid package's resources), enable it when prebuilts
 are ready.
 2. According to (1), its SDK_VERSION can be current)

Bug: 187404676
Test: TARGET_BUILD_UNBUNDLED_IMAGE m vendorimage, and check if there is
no build error regarding RRO.

Change-Id: I94e3122372dd20c942b2c858070a6ca797312792