Revert "Build and ship bindgen along with the Rust toolchain"

This reverts commit b82362661f1fac1954ba59580b7b4945c939215d.

Reason for revert:
Suspect for breaking linux_chromium_compile_dbg_ng

https://ci.chromium.org/ui/p/chromium/builders/try/linux_chromium_compile_dbg_ng/1553586/overview

Original change's description:
> Build and ship bindgen along with the Rust toolchain
>
> Remove bindgen and its dependencies from //third_party/rust,
> and have the GN scripts point to the binary from the toolchain
> package.
>
> This depends on a new Rust toolchain being built and updating
> the FALLBACK_REVISION to point to it, or the bindgen binary
> will simply go missing.
>
> Bug: 1426886
> Change-Id: I7ed5061c8ad0df30722be4406b73bc386ce75715
> Cq-Include-Trybots: luci.chromium.try:android-rust-arm32-rel,android-rust-arm64-dbg,android-rust-arm64-rel,linux-rust-x64-dbg,linux-rust-x64-rel
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4362520
> Reviewed-by: Collin Baker <[email protected]>
> Auto-Submit: danakj <[email protected]>
> Commit-Queue: Collin Baker <[email protected]>
> Cr-Commit-Position: refs/heads/main@{#1124972}

Bug: 1426886
Change-Id: I34648074ede4c1b11e526c1239fa1fb284133eef
Cq-Include-Trybots: luci.chromium.try:android-rust-arm32-rel,android-rust-arm64-dbg,android-rust-arm64-rel,linux-rust-x64-dbg,linux-rust-x64-rel
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4390873
Bot-Commit: Rubber Stamper <[email protected]>
Owners-Override: Ana Salazar Maldonado <[email protected]>
Commit-Queue: Ana Salazar Maldonado <[email protected]>
Auto-Submit: Ana Salazar Maldonado <[email protected]>
Cr-Commit-Position: refs/heads/main@{#1125001}
NOKEYCHECK=True
GitOrigin-RevId: 7cb9b57a98e1f6dd2f01787ef3e0fe05de5b0f8a

Author: anniefrchz