Remove module-lib and system-server from TARGET_AVAILABLE_SDK_VERSIONS

module-lib and system-server are not supported in Make, remove them
from TARGET_AVAILABLE_SDK_VERSIONS.

Also replace the hardcoded test_current version with the one found in
the prebuilts.

Fixes: 185903998
Test: get_build_var TARGET_AVAILABLE_SDK_VERSIONS
Change-Id: I745fbcf019092ec27a9903c48fdb95e892c02e3e