[HOTFIX] Patching maven build after #6 (SPARK-1121).

That patch removed the Maven avro declaration but didn't remove the
actual dependency in core. /cc @scrapcodes

Author: Patrick Wendell <pwendell@gmail.com>

Closes #37 from pwendell/master and squashes the following commits:

0ef3008 [Patrick Wendell] [HOTFIX] Patching maven build after #6 (SPARK-1121).

core/pom.xml

@@ -46,14 +46,6 @@
                 </exclusion>
             </exclusions>
         </dependency>
-        <dependency>
-            <groupId>org.apache.avro</groupId>
-            <artifactId>avro</artifactId>
-        </dependency>
-        <dependency>
-            <groupId>org.apache.avro</groupId>
-            <artifactId>avro-ipc</artifactId>
-        </dependency>
         <dependency>
             <groupId>org.apache.curator</groupId>
             <artifactId>curator-recipes</artifactId>