Reimplement $dist/updates vs $dist-security more backwards-compatible

This reverts most code, but not the implemented functionality of
commit 2fba5cb90e.

Requiring a config file change to still be able to install old
distributions would make a bump of the major version necessary
according to Semantic Versioning. Let's avoid that:

The list of distributions with the old path scheme is finite and will
never change again. Hence it's ok and especially backwards compatible
to hardcode this list in hooks/debian/20-setup-apt.

It's also less and more obvious (but not necessarily easier to read)
code. But it's all in one place and not scattered over three files.
And it's just one line instead like a dozen or two dozens.

Closes: #972749 (kinda again)

etc/distributions.conf

@@ -5,17 +5,17 @@
 # codename = distribution and further keywords
 #
 # Known distributions: debian, ubuntu
-# Known keywords: eol, pygrub, default-keyring, dont-test, security-subdir
+# Known keywords: eol, pygrub, default-keyring, dont-test
 # Known generic keywords: *.gpg (uses the according /usr/share/keyrings/….gpg file)
 #
-sarge        = debian security-subdir eol
-etch         = debian security-subdir eol
-lenny        = debian security-subdir eol
-squeeze      = debian security-subdir eol default-keyring
-wheezy       = debian security-subdir eol
-jessie       = debian security-subdir eol
-stretch      = debian security-subdir
-buster       = debian security-subdir
+sarge        = debian eol
+etch         = debian eol
+lenny        = debian eol
+squeeze      = debian eol default-keyring
+wheezy       = debian eol
+jessie       = debian eol
+stretch      = debian
+buster       = debian
 bullseye     = debian
 bookworm     = debian dont-test
 trixie       = debian dont-test

hooks/common.sh

@@ -422,24 +422,3 @@ installGentooPackage ()
     logMessage "NOTE: Not doing anything - this is a stub - FIXME"
 
 }
-
-
-
-
-#
-#  findDistributionConf path
-#
-# returns either a relative or an absolut path to distributions.conf
-#
-findDistributionsConf ()
-{
-    prefix=$1
-
-    if [ -f etc/distributions.conf ]; then
-        echo etc/distributions.conf
-    elif [ -f ${prefix:-}/etc/xen-tools/distributions.conf ]; then
-        echo ${prefix:-}/etc/xen-tools/distributions.conf
-    elif [ -f /etc/xen-tools/distributions.conf ]; then
-        echo /etc/xen-tools/distributions.conf
-    fi
-}

hooks/debian/20-setup-apt

@@ -20,7 +20,6 @@ else
     . ./hooks/common.sh
 fi
 
-distributions_conf=$(findDistributionsConf $prefix)
 
 #
 # Log our start
@@ -67,7 +66,7 @@ if ( test "${dist}" "!=" "sid" && test "${dist}" "!=" "unstable" && \
      test -e /etc/apt/sources.list && \
      grep ^deb.*security -r /etc/apt/sources.list /etc/apt/sources.list.d >/dev/null 2>/dev/null ) ; then
 
-    if fgrep "${dist}" $distributions_conf | fgrep -q security-subdir; then
+    if echo "${dist}" | egrep -q '\b(sarge|etch|lenny|squeeze|wheezyjessie|stretch|buster)\b'; then
 
         cat <<E_O_APT >> ${prefix}/etc/apt/sources.list
 #