Remove okhttp from top-level pom (apache-spark-on-k8s#166)

Author: foxish

pom.xml

@@ -333,11 +333,6 @@
         <artifactId>feign-jaxrs</artifactId>
         <version>${feign.version}</version>
       </dependency>
-      <dependency>
-        <groupId>com.squareup.okhttp3</groupId>
-        <artifactId>okhttp</artifactId>
-        <version>3.4.1</version>
-      </dependency>
       <dependency>
         <groupId>org.bouncycastle</groupId>
         <artifactId>bcpkix-jdk15on</artifactId>