Remove ref<>.

This type is unused and some parts of it has bitrot. In order to reduce
the complexity of new features, removing this.

Fixes: 131616631
Test: HIDL's test/run_all_device_tests.sh
Test: HIDL's test/run_all_host_tests.sh
Change-Id: Ic7c7f3eeeeba89fd1539faadbb9c69cf3fc0b7d7
3 files changed