derive_sdk: set min_sdk_version

Modules contributing mainline modules (APK/APEX) should set
min_sdk_version as well as apex_available.

Removed sdk_version because the sdk variant is not used by sdkext apex.
And, changed the dep from libbase_ndk to libbase. libbinder_ndk would
still work. But there's no reason to use it if not set sdk_version.

We could've set "sdk_variant_only" so that sdkext apex use the sdk
variant of derive_sdk explicitly. But even if we do that, we still have
to set min_sdk_version to be used by the apexes anyway.

Bug: 145796956
Test: m
Change-Id: I94ad8b9ffc5088822d3365253bf2f005a659d923