Always respect system_shared_libs from Android.bp

This commit removes a special case that ignores `system_shared_libs`
when `sdk_version`, `vendor_available`, or `vendor` is specified.

In the past, that special case was required for `libasync_safe` and
`libpropertyinfoparser`.  However, ignoring `system_shared_libs` meant
that we didn't have a way to skip the default libs when `sdk_version`
was specified.  This becomes a problem when the dependencies of
prebuilts are actually checked.  To be specific,
`libclang_rt.builtins-${arch}` falls into circular dependencies.

Bug: 123006819
Test: make checkbuild
Change-Id: I5fe038c00892b3abe5189b30d57ba59884b47cbb