Move MdnsResponseDecoder.Clock to MdnsUtils

This is a no-op change. The Clock class is a wrapper that is
used for testing. So move it from MdnsResponseDecoder to
MdnsUtils for subsequence metrics changes.

Bug: 287546772
Test: m
Change-Id: If4c8c0061c76ae26fc78a5ff463a31d57470fba0