build: use the standard `autoreconf` invocation

As version 0.20 of `autopoint` no longer overwrites 'extern-inline.m4',
there is no need any more for the custom calls of the various parts of
`autoreconf`.

This effectively reverts commit 4a1db96d from two and a half years ago.

autogen.sh

@@ -43,20 +43,11 @@ if [ "${gnulib_hash}" != "${curr_hash}" ]; then
 fi
 cd .. >/dev/null || exit 1
 
-echo "Autopoint..."
-autopoint --force
-
 rm -rf lib
 echo "Gnulib-tool..."
 ./gnulib/gnulib-tool --import ${modules}
 echo
 
-echo "Aclocal..."
-aclocal -I m4
-echo "Autoconf..."
-autoconf
-echo "Autoheader..."
-autoheader
-echo "Automake..."
-automake --add-missing
+echo "Autoreconf..."
+autoreconf --install --symlink --force
 echo "Done."