maint: Drop xz tarballs to reduce maintainer QA

* configure.ac (AM_INIT_AUTOMAKE): Remove dist-xz.
* README-alpha: Don't mention xz.
* bootstrap.conf (buildreq): Drop xz.

README-alpha

@@ -61,7 +61,6 @@ you have the latest stable version.
 - Texinfo <https://www.gnu.org/software/texinfo>
 - help2man <https://www.gnu.org/software/help2man>
 - ncurses <https://www.gnu.org/software/ncurses/> (optional, for talk)
-- xz <https://tukaani.org/xz/> (for 'make dist')
 - Texlive & epsf <http://www.tug.org/texlive/> (for 'make dist')
 
 * Building

bootstrap.conf

@@ -27,7 +27,6 @@ m4         -
 makeinfo   -
 help2man   -
 gzip	   -
-xz	   -
 "
 
 checkout_only_file=README-alpha

configure.ac

@@ -28,7 +28,7 @@ AC_CONFIG_AUX_DIR([build-aux])
 AC_CONFIG_HEADERS([config.h:config.hin])
 AC_CANONICAL_HOST
 
-AM_INIT_AUTOMAKE([1.11.1 dist-xz tar-ustar -Wall -Werror])
+AM_INIT_AUTOMAKE([1.11.1 tar-ustar -Wall -Werror])
 
 # For now, we always use libexecdir; later we may want to vary where
 # the daemons go.