Revert "Add common_type specializations for host_device refs to device and host refs."

This reverts commit 72a1161.

Author: bdice

cpp/include/rmm/resource_ref.hpp

@@ -137,53 +137,3 @@ static_assert(std::is_constructible_v<host_resource_ref, host_device_resource_re
 
 /** @} */  // end of group
 }  // namespace RMM_NAMESPACE
-
-// Specialize std::common_type to enable ternary operator type deduction.
-// A host_device resource can be used as either a device-only or host-only resource.
-namespace std {
-
-// host_device_async_resource_ref and device_async_resource_ref -> device_async_resource_ref
-template <>
-struct common_type<rmm::host_device_async_resource_ref, rmm::device_async_resource_ref> {
-  using type = rmm::device_async_resource_ref;
-};
-
-template <>
-struct common_type<rmm::device_async_resource_ref, rmm::host_device_async_resource_ref> {
-  using type = rmm::device_async_resource_ref;
-};
-
-// host_device_resource_ref and device_resource_ref -> device_resource_ref
-template <>
-struct common_type<rmm::host_device_resource_ref, rmm::device_resource_ref> {
-  using type = rmm::device_resource_ref;
-};
-
-template <>
-struct common_type<rmm::device_resource_ref, rmm::host_device_resource_ref> {
-  using type = rmm::device_resource_ref;
-};
-
-// host_device_async_resource_ref and host_async_resource_ref -> host_async_resource_ref
-template <>
-struct common_type<rmm::host_device_async_resource_ref, rmm::host_async_resource_ref> {
-  using type = rmm::host_async_resource_ref;
-};
-
-template <>
-struct common_type<rmm::host_async_resource_ref, rmm::host_device_async_resource_ref> {
-  using type = rmm::host_async_resource_ref;
-};
-
-// host_device_resource_ref and host_resource_ref -> host_resource_ref
-template <>
-struct common_type<rmm::host_device_resource_ref, rmm::host_resource_ref> {
-  using type = rmm::host_resource_ref;
-};
-
-template <>
-struct common_type<rmm::host_resource_ref, rmm::host_device_resource_ref> {
-  using type = rmm::host_resource_ref;
-};
-
-}  // namespace std