Use android::binder::unique_fd

This brings Binder's usage in Trusty closer to Linux Binder and will
enable dropping libbase dependency.

Bug: 302723053
Test: trusty/vendor/google/aosp/scripts/build.py generic-arm64-test-debug
Change-Id: I8909eac6be3b98e4bdbba0b60369b090adc9c21d