Remove java_sdk_library_import special-case in android/prebuilt.go

The top-level java_sdk_library_import module was special-cased in
android/prebuilt.go since its GenerateAndroidBuildActions creates the
build rules for hiddenapi and dexpreopt when prebuilt apexes are used
with source module sdk. These build rules have since been migrated to
the top-level `prebuilt_apex` and `apex_set`, so we can drop this
special-case now.

Test: m nothing --no-skip-soong-tests
Change-Id: Ifae7a7e99b01a1f5a6f327cb56680bac3ab276f7