Unset platform_apis if sdk_version is already set

Unsetting platform_apis while keeping sdk_version as is does not affect
the module's deps

Test: m queryview && builozer 'print soong_module_deps' :target (to
ensure the deps aren't affected

Bug: 219755537
Change-Id: Ic0d02c5e7fec24843e4cd2541cc5106381c7180e