Revert of Move fetching logic out of ApplicationManager, eliminate url mappings. (patchset #14 id:260001 of https://codereview.chromium.org/1342503003/ )

Reason for revert:
Broke the gn builds:
ERROR at //mojo/fetcher/about_fetcher_unittest.cc:17:11: Can't include this header from here.
#include "mojo/fetcher/about_fetcher.h"
          ^---------------------------
The target:
  //mojo/runner:mojo_runner_unittests
is including a file from the target:
  //mojo/fetcher:fetcher

It's usually best to depend directly on the destination target.
In some cases, the destination target is considered a subcomponent
of an intermediate target. In this case, the intermediate target
should depend publicly on the destination to forward the ability
to include headers.

Dependency chain (there may also be others):
  //mojo/runner:mojo_runner_unittests -->
  //mojo/runner:lib --[private]-->
  //mojo/fetcher:fetcher

https://build.chromium.org/p/chromium.linux/builders/Linux%20GN/builds/32017/steps/gn_check/logs/stdio

Original issue's description:
> Move fetching logic out of ApplicationManager, eliminate url mappings.
>
> BUG=
>
> Committed: https://crrev.com/7134773ceeef31531b84818158902e6d7c74f110
> Cr-Commit-Position: refs/heads/master@{#348659}
>
> Committed: https://crrev.com/c7ef4d2131963307ea537fc269bb5acee9383de2
> Cr-Commit-Position: refs/heads/master@{#348954}

[email protected],[email protected],[email protected]
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/1338283003

Cr-Commit-Position: refs/heads/master@{#348979}
48 files changed