btrfs-progs: tests: enhance invalid extent item generation test cases

This patch will:

- Add a new test image for fsck/044
  This new image has a corrupted extent item generation for tree block.
  This image can expose a bug in original mode, which can't detect the
  problem.
  This image also utilize the tree block generation detection code,
  which the existing image doesn't.

- Rename the existing image
  To reflect the fact that the existing one is only for data extent.

- Remove the test.sh
  So that the generic path will test both detection and repair.

Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

tests/fsck-tests/044-invalid-extent-item-generation/test.sh

@@ -1,19 +0,0 @@
-#!/bin/bash
-#
-# Due to a bug in --init-extent-tree option, we may create bad generation
-# number for data extents.
-#
-# This test case will ensure btrfs check can at least detect such problem,
-# just like kernel tree-checker.
-
-source "$TEST_TOP/common"
-
-check_prereq btrfs
-
-check_image() {
-	run_mustfail \
-		"btrfs check failed to detect invalid extent item generation" \
-		"$TOP/btrfs" check "$1"
-}
-
-check_all_images