Remove protobuf dumping support from FaceService

Currently, FaceService supports a `--proto` flag for dumping protobuf
debug data to GMS core. This functionality is now redundant and presents
a privacy risk, so this commit removes support for it and deletes the
associated method.

Test: manual
1. Attach a device and run `adb shell dumpsys face --proto`
2. Without change, verify that this prints out binary protobuf data
3. With change, verify that the output is the same as `adb shell dumpsys
face` and contains no protobuf data

Fixes: 135954555
Change-Id: I4cb6215cdba0f080259a5f08ae910d6bfc6c0c80