create_api_docs.dart: correct command logging (#155226)

The tool currently prints that the _dart_ command is run, and does not include the 'pub' sub-command. Something like:

```none
/private/var/folders/72/ltck4q353hsg3bn8kpkg7f84005w15/T/flutterzXpww6/bin/dart \
    global run --enable-asserts dartdoc
```

(newline mine)

But this is incorrect; the `runPubGet` function runs the _flutter_ command, and prepends `pub` to the list of arguments.

dev/tools/create_api_docs.dart

@@ -659,7 +659,8 @@ class DartdocGenerator {
 
     String quote(String arg) => arg.contains(' ') ? "'$arg'" : arg;
     print('Executing: (cd "${packageRoot.path}" ; '
-        '${FlutterInformation.instance.getDartBinaryPath().path} '
+        '${FlutterInformation.instance.getFlutterBinaryPath().path} '
+	'pub '
         '${dartdocArgs.map<String>(quote).join(' ')})');
 
     process = ProcessWrapper(await runPubProcess(
@@ -1086,13 +1087,6 @@ class FlutterInformation {
   @visibleForTesting
   static set instance(FlutterInformation? value) => _instance = value;
 
-  /// The path to the Dart binary in the Flutter repo.
-  ///
-  /// This is probably a shell script.
-  File getDartBinaryPath() {
-    return getFlutterRoot().childDirectory('bin').childFile('dart');
-  }
-
   /// The path to the Dart binary in the Flutter repo.
   ///
   /// This is probably a shell script.