Partially revert #8332 (#8386)

The JDK doesn't put `javac` in the PATH on Windows :(

packages/flutter_tools/lib/src/android/android_workflow.dart

@@ -70,11 +70,14 @@ class AndroidWorkflow extends DoctorValidator implements Workflow {
         String javaVersion;
 
         try {
-          printTrace('javac -version');
+          printTrace('java -version');
 
-          ProcessResult result = processManager.runSync(<String>['javac', '-version']);
-          if (result.exitCode == 0)
-            javaVersion = result.stderr.split('\n')[0];
+          ProcessResult result = processManager.runSync(<String>['java', '-version']);
+          if (result.exitCode == 0) {
+            javaVersion = result.stderr;
+            List<String> versionLines = javaVersion.split('\n');
+            javaVersion = versionLines.length >= 2 ? versionLines[1] : versionLines[0];
+           }
         } catch (error) {
         }
 
@@ -83,7 +86,7 @@ class AndroidWorkflow extends DoctorValidator implements Workflow {
               'No Java Development Kit (JDK) found; you can download the JDK from $_kJdkDownload.'
           ));
         } else {
-          messages.add(new ValidationMessage('Java Development Kit (JDK) found: $javaVersion'));
+          messages.add(new ValidationMessage(javaVersion));
           type = ValidationType.installed;
         }
       } else {