[dart2wasm] Simplify source map flag code in dart compile wasm

After [0] lands we can remove a workaround in `dart compile wasm` that
checks for `--extra-compiler-option=--no-source-maps`.

[0] https://github.com/flutter/flutter/pull/153417

Change-Id: I19f4da96e198d73e2309652aa2aa08d5e2c72d48
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/380461
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Ömer Ağacan <omersa@google.com>

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

@@ -809,13 +809,7 @@ class CompileWasmCommand extends CompileSubcommandCommand {
     handleOverride(optimizationFlags, 'minify',
         args.wasParsed('minify') ? args.flag('minify') : null);
 
-    bool generateSourceMap = args.flag('source-maps');
-    // TODO(kustermann): Remive this temporary change when flutter no longer
-    // uses --extra-compiler-option=--no-source-maps
-    if (extraCompilerOptions.any((o) => o == '--no-source-maps')) {
-      generateSourceMap = false;
-    }
-
+    final generateSourceMap = args.flag('source-maps');
     final enabledExperiments = args.enabledExperiments;
     final dart2wasmCommand = [
       sdk.dartAotRuntime,