Revert "Split read and write in ServiceWorkerRaceNetworkRequestURLLoaderClient"

This reverts commit 71a486e1.

Reason for revert: net::DraninableIOBuffer introduced crashes on Canary. crbug.com/327694512

Original change's description:
> Split read and write in ServiceWorkerRaceNetworkRequestURLLoaderClient
>
> This CL removes `ReadAndWrite()` and `ReadAndTwoPhaseWrite()`, and
> updates to call `Read()` and `Write()` (or, `TwoPhaseWrite()`)
> separately.
>
> After this CL, the read operation is called only when the read data pipe
> becomes readable (or the peer closed), and the write data pipe becomes
> writable. This would improve the code base that mojo data pipe APIs to
> be called in an appropriate timing.
>
> Also this CL updates `RaceNetworkRequestReadBufferManager::ReadData()`
> to be called only when the remaining unconsumed buffer does not exist
> for the simplicity.
>
> Bug: 40943349
> Change-Id: I78495ff75f96e7306f3920843b5ec3be24ea2d7d
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5332231


> Reviewed-by: Yoshisato Yanagisawa <yyanagisawa@chromium.org>
> Commit-Queue: Shunya Shishido <sisidovski@chromium.org>
> Reviewed-by: Kouhei Ueno <kouhei@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1266937}

Bug: 40943349
Change-Id: I97a523db0395c57813d781c9aa66b202bd0226fa
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5334166
Commit-Queue: Shunya Shishido <sisidovski@chromium.org>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Cr-Commit-Position: refs/heads/main@{#1267368}