Don't attempt to automatically set the default region

This failed in cases where the default region isn't configured anywhere (e.g.
in our travis builds...)

Author: Bryan Donlan

src/main/java/com/amazonaws/encryptionsdk/kms/KmsMasterKeyProvider.java

@@ -71,7 +71,7 @@ public interface RegionalClientSupplier {
     }
 
     public static class Builder implements Cloneable {
-        private String defaultRegion_ = new DefaultAwsRegionProviderChain().getRegion();
+        private String defaultRegion_ = null;
         private RegionalClientSupplier regionalClientSupplier_ = null;
         private AWSKMSClientBuilder templateBuilder_ = null;
         private List<String> keyIds_ = new ArrayList<>();

src/test/java/com/amazonaws/services/kms/KMSProviderBuilderIntegrationTests.java

@@ -154,45 +154,4 @@ public void whenBogusEndpointIsSet_constructionFails() throws Exception {
     public void whenDefaultRegionSet_itIsUsedForBareKeyIds() throws Exception {
         // TODO: Need to set up a role to assume as bare key IDs are relative to the caller account
     }
-
-    @Test
-    public void whenDefaultRegionIsNotSet_providerChainDefaultIsUsed() throws Exception {
-        assertDefaultRegionConsistency();
-
-        String oldRegion = System.getProperty("aws.region");
-        Assume.assumeFalse("Can't change env variables from within Java", System.getenv("AWS_REGION") != null);
-
-        try {
-            System.setProperty("aws.region", "eu-central-1");
-            assertEquals("eu-central-1", getInitialDefaultRegion());
-
-            System.setProperty("aws.region", "us-west-2");
-            assertEquals("us-west-2", getInitialDefaultRegion());
-
-        } finally {
-            if (oldRegion != null) {
-                System.setProperty("aws.region", oldRegion);
-            } else {
-                System.clearProperty("aws.region");
-            }
-        }
-    }
-
-    private void assertDefaultRegionConsistency() throws Exception {
-        String initialDefault = getInitialDefaultRegion();
-
-        assertEquals(
-                new DefaultAwsRegionProviderChain().getRegion(),
-                initialDefault
-        );
-    }
-
-    private String getInitialDefaultRegion() throws NoSuchFieldException, IllegalAccessException {
-        KmsMasterKeyProvider.Builder builder = KmsMasterKeyProvider.builder();
-
-        Field f = KmsMasterKeyProvider.Builder.class.getDeclaredField("defaultRegion_");
-        f.setAccessible(true);
-
-        return (String) f.get(builder);
-    }
 }