This reverts commit 094202bb91.
Reason for revert: Break flutter, this change should happen after
flutter being migrated to the same gn-sdk.
Original change's description:
> [Fuchsia] Remove the legacy gn build rules for fuchsia
>
> The updated test-scripts contains https://crrev.com/c/5341620 which
> allows to generate fidl apis with an env var controlled location
> rather than a hard-coded one. So the existing fuchsia gn build rules
> in dart/sdk become obsolete and can be fully removed in favor of the
> one in //third_party/fuchsia/gn-sdk/.
>
> Meanwhile the gn-sdk has been updated with
> https://crrev.com/c/5325282 to use api-level version'ed idk but not
> the ones in arch/.
>
> Cq-Include-Trybots: luci.dart.try:vm-fuchsia-release-arm64-try,vm-fuchsia-release-x64-try
> Tested: ^^^^^
> Bug: 40935282
> Change-Id: I2ce958e6db1ff8221beef7b7ff953c32bb4525ba
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/355283
> Reviewed-by: Ryan Macnak <rmacnak@google.com>
> Reviewed-by: Alexander Thomas <athom@google.com>
> Commit-Queue: Zijie He <zijiehe@google.com>
Bug: 40935282
Change-Id: I7c455d1d362210523671c97d99ef018ede1743f4
Cq-Include-Trybots: luci.dart.try:vm-fuchsia-release-arm64-try,vm-fuchsia-release-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/356307
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Zijie He <zijiehe@google.com>
Reviewed-by: Derek Xu <derekx@google.com>
Commit-Queue: Zijie He <zijiehe@google.com>
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