Set iterator and range detach operations to noop

Leave the housekeeping to the NSHashTable itself, which should purge
null-references automatically (not necessarily right away)

Also update tests accordingly: Use `allObjects.count` instead of simply
`count` on the NSHashTable, since `allObjects.count` returns non-null
references.

This should fix #36

Tests/HTMLKitTests/HTMLRangeTests.m

@@ -2112,10 +2112,10 @@
 	@autoreleasepool {
 		HTMLRange *range = [[HTMLRange alloc] initWithDocument:document];
 		[range cloneContents];
-		XCTAssertEqual(1, ranges.count);
+		XCTAssertEqual(1, ranges.allObjects.count);
 	}
 
-	XCTAssertEqual(0, ranges.count);
+	XCTAssertEqual(0, ranges.allObjects.count);
 }
 
 @end