[dart2wasm] Remove --turboshaft-wasm flag (which was removed from D8)…

… in test runner

Running tests currently result in a warning by D8:

    Warning: unknown flag --turboshaft-wasm.

Turboshaft was enabled by default in V8 and is no longer exposed as a
flag.

Change-Id: I487f145ba60b20d7c61397c4ad4c5af1d0263b60
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/404320
Reviewed-by: Ömer Ağacan <[email protected]>
Commit-Queue: Martin Kustermann <[email protected]>

pkg/test_runner/lib/src/compiler_configuration.dart

@@ -609,7 +609,6 @@ class Dart2WasmCompilerConfiguration extends CompilerConfiguration {
     final isD8 = runtimeConfiguration is D8RuntimeConfiguration;
     return [
       if (isD8) ...[
-        '--shell-option=--turboshaft-wasm',
         '--shell-option=--experimental-wasm-imported-strings',
       ],
       wasmFilename,