Hardcode Scala Version

## What changes were proposed in this pull request?
This is a patch to get around the fact that we have a different deployment mode from upstream Spark. Patch initially authored by marmbrus.

Author: Michael Armbrust <michael@databricks.com>

Closes apache#42 from rxin/rxin-hardcode-scala-version.

launcher/src/main/java/org/apache/spark/launcher/AbstractCommandBuilder.java

@@ -228,18 +228,8 @@ String getScalaVersion() {
     String scala = getenv("SPARK_SCALA_VERSION");
     if (scala != null) {
       return scala;
-    }
-    String sparkHome = getSparkHome();
-    File scala210 = new File(sparkHome, "launcher/target/scala-2.10");
-    File scala211 = new File(sparkHome, "launcher/target/scala-2.11");
-    checkState(!scala210.isDirectory() || !scala211.isDirectory(),
-      "Presence of build for both scala versions (2.10 and 2.11) detected.\n" +
-      "Either clean one of them or set SPARK_SCALA_VERSION in your environment.");
-    if (scala210.isDirectory()) {
-      return "2.10";
     } else {
-      checkState(scala211.isDirectory(), "Cannot find any build directories.");
-      return "2.11";
+      return "2.10";
     }
   }