net: cleanup unused things from network_interfaces header file
net: cleanup unused things from network_interfaces header file

This patch removes a bunch of unused includes and forward declarations
that are not used by any function/class in this header file.

BUG=None
R=eroman@chromium.org

Review URL: https://codereview.chromium.org/1563853003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#368058}

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