Revert "`span`-ification: `mojo::DataPipe[Consumer|Producer]Handle`: New API."

This reverts commit a23daf4f.

Reason for revert: Causing MSAN issues on https://ci.chromium.org/ui/p/chromium/builders/ci/Linux%20ChromiumOS%20MSan%20Tests/43854/test-results?sortby=&groupby=

Original change's description:
> `span`-ification: `mojo::DataPipe[Consumer|Producer]Handle`: New API.
>
> This CL `span`-ifies the APIs in `mojo/public/cpp/system/data_pipe.h`:
>
> * `BeginReadData` and `BeginWriteData` return (via an out parameter)
>   a `span` instead of returning a ptr+size pair.
> * `ReadData` and `WriteData` consume a `span` instead of consuming
>   a ptr+size pair.
>
> This CL adds the new APIs + coverts callers under `//mojo`.
>
> For more details see the design note here:
> https://docs.google.com/document/d/1c4NKpXwpQ9MKK1SbJ4C6MvhXI8-KJZ4jq7N4VHTHJoI/edit?usp=sharing
>
> Bug: 40284755
> Change-Id: I70a7fab6e57eb3481305e82dd504de91042fa881
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5598233


> Auto-Submit: Łukasz Anforowicz <lukasza@chromium.org>
> Reviewed-by: Daniel Cheng <dcheng@chromium.org>
> Commit-Queue: Daniel Cheng <dcheng@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#1313022}

Bug: 40284755
Change-Id: Ifcd3706b24c7842d4bba7065a625b5b3ec9739b4
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5619490
Owners-Override: Darren Shen <shend@chromium.org>
Commit-Queue: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Darren Shen <shend@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1313154}