Revert "bzip2/xz: use the prebuilts."

This reverts commit e114b3f0.

Build broke as follows:

out/soong/host/linux-x86/bin/sbox --sandbox-path out/soong/.temp --output-root out/soong/.intermediates/system/update_engine/ue_unittest_disk_imgs/gen -c 'tar -jxf system/update_engine/sample_images/sample_images.tar.bz2 -C __SBOX_OUT_DIR__/gen disk_ext2_1k.img disk_ext2_4k.img disk_ext2_4k_empty.img disk_ext2_unittest.img' __SBOX_OUT_DIR__/gen/disk_ext2_1k.img __SBOX_OUT_DIR__/gen/disk_ext2_4k.img __SBOX_OUT_DIR__/gen/disk_ext2_4k_empty.img __SBOX_OUT_DIR__/gen/disk_ext2_unittest.img 
"bzip2" is not allowed to be used. See https://android.googlesource.com/platform/build/+/master/Changes.md#PATH_Tools for more information. 
tar: Child returned status 1 
tar: Error is not recoverable: exiting now 
sbox command (tar -jxf system/update_engine/sample_images/sample_images.tar.bz2 -C out/soong/.temp/sbox849645882/gen disk_ext2_1k.img disk_ext2_4k.img disk_ext2_4k_empty.img disk_ext2_unittest.img) failed with err "exit status 2" 

Change-Id: I3fe7100886ea3b748f5a6b5fc6d2811391bb72a8