Use existing SPDX identifier for GPL-2.0-only WITH Classpath-exception-2.0

List of licenses is [here](https://spdx.org/licenses/), list of exceptions is [here](https://spdx.org/licenses/exceptions-index.html).

build/conf/license.conf

@@ -76,7 +76,6 @@ LICENSES_UNATTRIBUTED= \
     Go-License \
     Google-Patent-License-Webm \
     Google-Patent-License-Webrtc \
-    GPL-2.0 WITH Classpath-exception-2.0 \
     GPL-2.0-only WITH Classpath-exception-2.0 \
     GPL-2.0 WITH FOSS-exception \
     GPL-2.0-only WITH freertos-exception-2.0 \