Remove deprecated / delete dist-lzma from configure.ac

Upstream autotools has removed dist-lzma as of 2.69; this prevents generating a configure script with the following error:

    $ autoreconf -i
    configure.ac:6: error: support for lzma-compressed distribution archives has been removed
    ... ellided install output ...
    autoreconf: automake failed with exit status: 1

See the automake manpages for more info.