Remove obsolete Debian notes from HACKING

The HACKING document says that Debian's automake version doesn't satisfy
the automake >= 1.10 requirement, but this is no longer true. The
automake version in Debian 8 (oldstable) is 1.14 and the version in
Debian 9 (stable) is 1.15.
diff --git a/HACKING b/HACKING
index 87762f1..e10986f 100644
--- a/HACKING
+++ b/HACKING
@@ -5,16 +5,7 @@
 ========================
 
 When building and testing directly from the repository it is important to
-have at least automake version 1.10 or later installed. All modern
-distributions should default to the latest version, but it seems that
-Debian's default is still an earlier version:
-
-  Check version
-    # dpkg -l '*automake*'
-
-  Install new version
-    # apt-get install automake1.10
-    # update-alternatives --config automake
+have at least automake version 1.10 or later installed.
 
 
 Working with the source code repository