Revert "RtpSender: Create the Sframe encryptor and hand out a worker proxy"

This reverts commit 8354b7c19d32a3dbe7268319af6085e6ec9ec099.

Reason for revert: breaks webrtc-internal bot. Compile error in sframe

Failure Link: https://fusion2.corp.google.com/invocations/e9a2a344-3234-4d69-a6e9-b95f8700b396/targets/%2F%2Fthird_party%2Fwebrtc:webrtc_all_cc/log?q=label:session_id%3Dbtbs-224212c0-8627-4ddc-9137-60e85c0d9b6c

Original change's description:
> RtpSender: Create the Sframe encryptor and hand out a worker proxy
>
> Implements `RtpSenderBase::CreateSframeEncryptorOrError`
>
> When called, it creates a `SframeEncryptor` on the worker thread and —
> if an SSRC is already assigned — immediately pushes it to the media
> channel via `SetSframeEncryptor`. If the SSRC is not yet known,
> `SetSsrc` is updated to push the encryptor to the channel once an SSRC
> is assigned.
>
> The returned `SframeEncryptorInterface` is wrapped in a new
> `SframeEncryptorProxy` that marshals `SetEncryptionKey` calls to the
> worker thread, so callers can safely invoke it from any other thread.
>
> Bug: webrtc:479862368
> Change-Id: Ic647c4658fa672c820d09a13c34ee0b158f3ae89
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/493780
> Commit-Queue: Björn Terelius <terelius@webrtc.org>
> Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
> Reviewed-by: Björn Terelius <terelius@webrtc.org>
> Cr-Commit-Position: refs/heads/main@{#48542}

Bug: webrtc:479862368
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Change-Id: I7e24587bf67f8f4a5f85a29c672fbccc22a566b8
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/501520
Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Ilya Nikolaevskiy <ilnik@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#48544}