Revert "Reland "[ VM / DartDev ] Launch DartDev in an isolate within a single main Dart process""

This reverts commit bc4cb123a8468d5ae27749fae5382b9f91379428.

Reason for revert: breaks crossword simarm tests https://ci.chromium.org/p/dart/builders/ci.sandbox/vm-kernel-precomp-linux-debug-simarm_x64/2619

Original change's description:
> Reland "[ VM / DartDev ] Launch DartDev in an isolate within a single main Dart process"
> 
> This CL changes how DartDev is run and how the run command handles executing a Dart program (will port additional commands in a separate CL). Rather than using DartDev to spawn a child process to run user code, the VM will instead launch a DartDev isolate after doing some VM options processing. DartDev will communicate information like exit codes and script/arg pairs with the VM via isolate ports. Once DartDev runs to completion and notifies the VM that a script should be run, the VM will move on to spawning another isolate with user code and continue executing in the same VM process.
> 
> By moving DartDev into an isolate within the same process that user code will eventually run in we're able to resolve the following issues that arose due to signal handling and IPC issues:
> 
> VM hangs when --enable-vm-service is supplied and there are compile time errors (https://github.com/dart-lang/sdk/issues/42630)
> Dart daemon spinning in exit code handler / zombie Dart processes (https://github.com/dart-lang/sdk/issues/41978)
> Signal handling in children of 'dartdev run' is problematic (https://github.com/dart-lang/sdk/issues/42092)
> 
> This reverts commit 3849b5061c489ab079598075a9c8caae907f97b0.
> 
> Change-Id: I4fd3ba33840771a9f284d733c4a25fac6cde64ca
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/154706
> Reviewed-by: Siva Annamalai <asiva@google.com>

TBR=bkonyi@google.com,asiva@google.com

Change-Id: I649d94c668417f2edbfd7039fa5c876e10dc32fe
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/154800
Reviewed-by: Alexander Aprelev <aam@google.com>