debian: Update documentation to reflect package matching upstream

Now that the library matches a standard upstream release, we do not
need to document differences from the upstream ABI in the Debian
README.
diff --git a/debian/changelog b/debian/changelog
index 3fc3992..9317f3a 100644
--- a/debian/changelog
+++ b/debian/changelog
@@ -1,16 +1,16 @@
 xz-utils (5.2.4-0.1) unstable; urgency=low
 
   * New upstream release.  Closes: #851615.
-  * Drop -lfreebsd-glue patch, fixed differently upstream.
-    - No longer Build-Depends: freebsd-glue on kfreebsd.
+  * Drop patches; all were applied or otherwise fixed upstream.
+  * No longer Build-Depends: freebsd-glue on kfreebsd.
   * liblzma:
     - Remove compatibility tricks that permit sharing a process with
       liblzma.so.2.  This means liblzma.a no longer depends on libdl
       at run time.
       Closes: #919950.  Thanks to Josh Triplett.
     - Breaks: liblzma2 versions without symbol versioning.
-  * xz-utils:
-    - README.Debian: Remove notes about liblzma.so.2 compatibility.
+  * xz-utils/README.Debian: Remove notes about differences from
+    upstream.
 
  -- Jonathan Nieder <jrnieder@gmail.com>  Sun, 27 Jan 2019 15:02:13 -0800
 
diff --git a/debian/xz-utils.README.Debian b/debian/xz-utils.README.Debian
index 7a06d2b..77633ef 100644
--- a/debian/xz-utils.README.Debian
+++ b/debian/xz-utils.README.Debian
@@ -3,9 +3,8 @@
 
 Contents:
  1. History
- 2. Differences from standard XZ Utils
- 3. LZMA Utils compatibility
- 4. Configuration
+ 2. LZMA Utils compatibility
+ 3. Configuration
 
 History
 -------
@@ -15,40 +14,6 @@
 of magic number, but it gets enough use to still need to be supported.
 See /usr/share/doc/xz-utils/history.txt.gz for the full story.
 
-Differences from standard XZ Utils
-----------------------------------
-
-XZ Utils 5.1.y has some experimental features which are disabled in
-Debian to allow interfaces to evolve.
-
-abi-threaded-encoder
-  Disable threaded compression in liblzma and xz.
-
-abi-version-script
-  liblzma: Do not pretend to satisfy dependencies on XZ_5.1.1alpha.
-
-man-date, man-xz-lvv-minver (from upstream)
-  Document the "Minimum version required to decompress" field of
-  "xz --robot -v -v --list" output.
-
-xz-lvv-empty-block-minver (from upstream)
-  Fix the version number printed by "xz -lvv" for files with Blocks
-  of zero uncompressed_size: the decoder bug preventing reading such
-  files was fixed in xz 5.0.2, not 5.0.3.
-
-decoder-check-first-0x00 (from upstream)
-  Check that the first byte of range encoded data is zero to catch
-  broken files sooner.
-
-Changes in 5.1.2alpha not applied:
-
-  Docs: Language fix to 01_compress_easy.c
-  xz: Add incomplete support for --block-list
-  INSTALL: Document --enable-symbol-versions
-  configure: Add a comment about *-linux tuples for clarity
-  TODO: Warn that threads and fork() do not mix well
-  Bump the version number and update NEWS for 5.1.2alpha
-
 LZMA Utils compatibility
 ------------------------
 
@@ -79,4 +44,4 @@
 
 See the "Memory usage" section of the xz(1) manual page for details.
 
- -- Jonathan Nieder <jrnieder@gmail.com>  Mon, 10 Sep 2012 14:35:27 -0700
+ -- Jonathan Nieder <jrnieder@gmail.com>  Sun, 27 Jan 2019 15:32:33 -0800