Remove BytesToBytesMap.finalize()

This is no longer necessary now that we do leak
detection and cleanup at higher levels (as part of MemoryManager).

Author: JoshRosen

unsafe/src/main/java/org/apache/spark/unsafe/map/BytesToBytesMap.java

@@ -157,16 +157,6 @@ public BytesToBytesMap(
     this(memoryManager, initialCapacity, 0.70, enablePerfMetrics);
   }
 
-  @Override
-  protected void finalize() throws Throwable {
-    try {
-      // In case the programmer forgot to call `free()`, try to perform that cleanup now:
-      free();
-    } finally {
-      super.finalize();
-    }
-  }
-
   /**
    * Returns the number of keys defined in the map.
    */

unsafe/src/test/java/org/apache/spark/unsafe/map/AbstractBytesToBytesMapSuite.java

@@ -95,11 +95,15 @@ private static boolean arrayEquals(
   @Test
   public void emptyMap() {
     BytesToBytesMap map = new BytesToBytesMap(memoryManager, 64);
-    Assert.assertEquals(0, map.size());
-    final int keyLengthInWords = 10;
-    final int keyLengthInBytes = keyLengthInWords * 8;
-    final byte[] key = getRandomByteArray(keyLengthInWords);
-    Assert.assertFalse(map.lookup(key, BYTE_ARRAY_OFFSET, keyLengthInBytes).isDefined());
+    try {
+      Assert.assertEquals(0, map.size());
+      final int keyLengthInWords = 10;
+      final int keyLengthInBytes = keyLengthInWords * 8;
+      final byte[] key = getRandomByteArray(keyLengthInWords);
+      Assert.assertFalse(map.lookup(key, BYTE_ARRAY_OFFSET, keyLengthInBytes).isDefined());
+    } finally {
+      map.free();
+    }
   }
 
   @Test