Migrate //remoting/protocol to net::CompletionRepeatingCallback

While working on CL1524492, I've found that nearly all the occurrences of
net::CompletionCallback required repeating callbacks, so this is a quick
CL to make that explicit, and use net::CompletionRepeatingCallback().

Bug: 714018, 807724
Change-Id: Ib5e05a3ff4da15206e63f8d0eff545919d9e9b6b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1529052
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Mario Sanchez Prada <mario@igalia.com>
Cr-Commit-Position: refs/heads/master@{#641772}
7 files changed