Revert "Temporary add 'RTPVideoHeaderH264::nalus_length'."

This reverts commit 04dd95fcac549fbdc330cee1de65074961db5934.

Reason for revert: code has been updated

Original change's description:
> Temporary add 'RTPVideoHeaderH264::nalus_length'.
>
> This is a forward fix for https://webrtc-review.googlesource.com/c/src/+/354622 that breaks client code using nalus_length.
>
> No-Try: true
> Change-Id: Ic0fc41696e408adefe4eb8792150a64b1eab49da
> Bug: None
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/354840
> Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
> Commit-Queue: Jeremy Leconte <jleconte@google.com>
> Owners-Override: Jeremy Leconte <jleconte@google.com>
> Cr-Commit-Position: refs/heads/main@{#42493}

Bug: None
Change-Id: I1b65fe94ca07efdb8c7643e2ac46517050095018
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/354860
Commit-Queue: Jeremy Leconte <jleconte@google.com>
Bot-Commit: rubber-stamper@appspot.gserviceaccount.com <rubber-stamper@appspot.gserviceaccount.com>
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#42496}