Revert "MFV: xz 5.6.0"

This commit reverts 8db56defa766eacdbaf89a37f25b11a57fd9787a,
rolling back the vendor import of xz 5.6.0 and restoring the
package to version 5.4.5.

The revert was not directly due to the attack (CVE-2024-3094):
our import process have removed the test cases and build scripts
that would have enabled the attack. However, reverting would
help to reduce potential confusion and false positives from
security scanners that assess risk based solely on version
numbers.

Another commit will follow to restore binary compatibility with
the liblzma 5.6.0 library by making the previously private
symbol (lzma_mt_block_size) public.

PR: 278127
MFC after: 3 days

MFV: xz 5.6.0.

MFC after: 2 weeks

MFV: xz 5.4.2.

MFC after: 2 weeks

MFV r333779: xz 5.2.4.

MFC after: 2 weeks

Import of liblzma, xz, xzdec, lzmainfo from vendor branch
Add support for xz and lzma to lesspipe.sh (xzless, lzless)
Bump __FreeBSD_version

Approved by: delphij (mentor)
MFC after: 2 weeks

MFV: xz 5.4.2.

MFC after: 2 weeks

MFV r333779: xz 5.2.4.

MFC after: 2 weeks

Import of liblzma, xz, xzdec, lzmainfo from vendor branch
Add support for xz and lzma to lesspipe.sh (xzless, lzless)
Bump __FreeBSD_version

Approved by: delphij (mentor)
MFC after: 2 weeks

A new jail(8) with a configuration file, to replace the work currently done
by /etc/rc.d/jail.

MFC r207842, r207844, r208099:

MFC r207842:
Import of liblzma, xz, xzdec, lzmainfo from vendor branch
Add support for xz and lzma to lesspipe.sh (xzless, lzless)

MFC r207844:
Add two public headers missing in r207842
Adjust CFLAGS for lzmainfo, xz, xzdec

MFC r208099:
Add versioned symbols to liblzma
Use default SHLIB_MAJOR.

Approved by: delphij (mentor)