Make derive_sdk_prefer32 uninstallable

Fix TARGET_BUILD_APPS builds by marking derive_sdk_prefer32
uninstallable so it doesn't try to create a rule to install to
the same path as derive_sdk.

Fixes: 153602595
Test: m TARGET_BUILD_APPS=foo nothing
Test: m test_com.android.sdkext &&
      deapexer list out/target/product/vsoc_x86/obj/ETC/test_com.android.sdkext_intermediates/test_com.android.sdkext.apex
Change-Id: I02bcbc0cbfef6ef66a79ad2ccd73c8af101b67de