[cleanup] remove unused code

- remove unused utility testing function
- remove leftover FLINK_CONF_DIR jvm property

This closes #2325

flink-clients/src/main/java/org/apache/flink/client/CliFrontend.java

@@ -1058,8 +1058,7 @@ public class CliFrontend {
 	// --------------------------------------------------------------------------------------------
 
 	public static String getConfigurationDirectoryFromEnv() {
-		String envLocation = System.getenv(ConfigConstants.ENV_FLINK_CONF_DIR);
-		String location = envLocation != null ? envLocation : System.getProperty(ConfigConstants.ENV_FLINK_CONF_DIR);
+		String location = System.getenv(ConfigConstants.ENV_FLINK_CONF_DIR);
 
 		if (location != null) {
 			if (new File(location).exists()) {

flink-core/src/test/java/org/apache/flink/api/common/ExecutionConfigTest.java

@@ -18,10 +18,8 @@
 
 package org.apache.flink.api.common;
 
-import org.apache.flink.util.SerializedValue;
 import org.junit.Test;
 
-import java.io.IOException;
 import java.util.Arrays;
 import java.util.List;
 
@@ -66,15 +64,4 @@ public class ExecutionConfigTest {
 		assertEquals(parallelism, config.getParallelism());
 	}
 
-	/**
-	 * Helper function to create a new ExecutionConfig for tests.
-	 * @return A serialized ExecutionConfig
-	 */
-	public static SerializedValue<ExecutionConfig> getSerializedConfig() {
-		try {
-			return new SerializedValue<>(new ExecutionConfig());
-		} catch (IOException e) {
-			throw new RuntimeException("Couldn't create new ExecutionConfig for test.", e);
-		}
-	}
 }