The function IndexDescriptor::getDefaultIndexVersion accepts a featureCompatibilityVersion parameter, but does nothing with it. In an attempt to reduce direct accesses to the fCV version parameter in SERVER-30745, this function should remove the argument and return the default.

IndexVersion IndexDescriptor::getDefaultIndexVersion(
    ServerGlobalParams::FeatureCompatibility::Version featureCompatibilityVersion) {
    return IndexVersion::kV2;
}

As a result, the calls to serverGlobalParams.featureCompatibility.getVersion() in database_impl.cpp, index_key_validate.cpp, and drop_indexes.cpp should be removed.