Disable stub validation when `WITHOUT_CHECK_API=true`

Even when building stubs from source, the rules for the
java_api_library modules are generated although they are not
executed. This leads to NPE, as setting `WITHOUT_CHECK_API=true`
prevents `checkCurrentApiTimestamp`, which the java_api_library modules
depend on, from being generated.

To prevent the NPE, this change prevents the `checkCurrentApiTimestamp`
from being registered as the dependency of the java_api_library modules
when `WITHOUT_CHECK_API=true` is set.

Test: BUILD_FROM_SOURCE_STUB=true WITHOUT_CHECK_API=true m nothing
Bug: 320601440
Change-Id: I4f19e30d9cd74bdc20dde0d14884fb03ff223ccb