Revert "When analyzer_cli is given --preview-dart-2, use KernelDriver."

This reverts commit 7d28e6fc21.

Reason for revert: <INSERT REASONING HERE>

Original change's description:
> When analyzer_cli is given --preview-dart-2, use KernelDriver.
> 
> R=​brianwilkerson@google.com, paulberry@google.com
> 
> Bug:
> Change-Id: I91484f906a691fba80917f8fd8ec1c0628c0815f
> Reviewed-on: https://dart-review.googlesource.com/14505
> Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
> Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

TBR=paulberry@google.com,scheglov@google.com,brianwilkerson@google.com

Change-Id: Ib440303cd82d6ebb14ef7d14efdb6b535cc0bf88
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/14580
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analyzer/lib/src/dart/analysis/kernel_context.dart

@@ -148,10 +148,8 @@ class KernelContext {
       }
 
       if (DEBUG) {
-        print('----------- ${targetLibrary.uriStr}');
         var libraryKernel = libraryMap[targetLibrary.uriStr];
         print(_getLibraryText(libraryKernel));
-        print('--------------------------------------');
       }
 
       // Create and configure a new context.

pkg/analyzer_cli/lib/src/driver.dart

@@ -650,8 +650,7 @@ class Driver implements CommandLineStarter {
           new FileContentOverlay(),
           null,
           context.sourceFactory,
-          context.analysisOptions,
-          enableKernelDriver: options.previewDart2);
+          context.analysisOptions);
       analysisDriver.results.listen((_) {});
       analysisDriver.exceptions.listen((_) {});
       scheduler.start();