Remove settings option for index store compression, compression is always enabled

closes elastic#2577

Author: kimchy

src/main/java/org/elasticsearch/common/compress/CompressedDirectory.java

@@ -26,7 +26,9 @@
 import java.io.IOException;
 
 /**
+ * @deprecated Used only for backward comp. to read old compressed files, since we now use codec based compression
  */
+@Deprecated
 public abstract class CompressedIndexInput<T extends CompressorContext> extends IndexInput {
 
     private IndexInput in;