Revert of Convert //net and //chromecast to std::unordered_* (patchset #5 id:80001 of https://codereview.chromium.org/1869503003/ )

Reason for revert:
Speculatively reverting this since it was in the blamelist https://chromium.googlesource.com/chromium/src/+log/39399be2c6a0063520d8d9b289e8f7b31e1eb094%5E..4241ad1dee5396c329a5e9379c3db3027f1b6456?pretty=fuller that I came up with after analyzing the content_browsertests failures (DownloadContentTest) on
https://build.chromium.org/p/chromium.linux/builders/Linux%20Tests%20%28dbg%29%281%29%2832%29/builds/27572 and https://build.chromium.org/p/chromium.memory/builders/Linux%20Chromium%20OS%20ASan%20LSan%20Tests%20%281%29/builds/11573

Original issue's description:
> Convert //net and //chromecast to std::unordered_*
>
> Do //chromecast at the same time as //net since there aren't many
> uses in //chromecast and one needs to be changed to mirror a //net
> API change.
>
> BUG=576864,554287
>
> Committed: https://crrev.com/4241ad1dee5396c329a5e9379c3db3027f1b6456
> Cr-Commit-Position: refs/heads/master@{#386485}

[email protected],[email protected],[email protected]
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=576864,554287

Review URL: https://codereview.chromium.org/1884453002

Cr-Commit-Position: refs/heads/master@{#386624}
54 files changed