Revert "[dart2wasm] Also use --traps-never-happen in deferred loading mode"

This reverts commit 6bcbc740e5.

Reason for revert: Broke pkg/dart2wasm/test/ir_test

Original change's description:
> [dart2wasm] Also use --traps-never-happen in deferred loading mode
>
> The dar2wasm compiler - when used in -O2 sound mode - should guarantee
> that no wasm traps happen. So we should  be able to use
> `--traps-never-happen` in deferred loading mode just like in normal
> mode.
>
> This saves around 1.2% in ACX Gallery
>
> Change-Id: I3d214b636b0bc2e8b18c2ef8c4bf0c86b19c23c8
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/458720
> Commit-Queue: Martin Kustermann <kustermann@google.com>
> Reviewed-by: Nate Biggs <natebiggs@google.com>

Change-Id: If51986574a7dc587b64b258278d763d51b3d28df
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/458900
Commit-Queue: Paul Berry <paulberry@google.com>
Reviewed-by: Nicholas Shahan <nshahan@google.com>
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Auto-Submit: Paul Berry <paulberry@google.com>

pkg/dartdev/lib/src/commands/compile.dart

@@ -765,7 +765,6 @@ class CompileWasmCommand extends CompileSubcommandCommand {
 
       --no-inline=*<noInline>*
 
-      --traps-never-happen
       -Os
     '''); // end of binaryenFlagsDeferredLoading