Move wrapPassthroughInternal out of headers.

Move implementation of wrapPassthroughInternal into
sources. Still provide a templated version for
convenient use (which should be optimized out
when not used).

This function:
- isn't template specific
- duplication takes up space on device/in-memory

Test: hidl's run_all_device_tests.sh
Bug: 33754152
Change-Id: I9e949f953732d843053ac5d6655700d48eda3190
3 files changed