Update AC_PROG_LIBTOOL to LT_INIT in configure.ac

Merged Mike Fleetwood requested to merge mfleetwo/gparted:obsolete-macro into master

Quoting the commit message

Autoconf 2.71 on Fedora 36 and Ubuntu 22.04 LTS has started reporting
a number of warnings about configure.ac containing obsolete macros.  One
of them is this:
    $ ./autogen.sh
    Processing ./configure.ac
    configure.ac:17: warning: The macro `AC_PROG_LIBTOOL' is obsolete.
    configure.ac:17: You should run autoupdate.
    m4/libtool.m4:99: AC_PROG_LIBTOOL is expanded from...
    configure.ac:17: the top level
Edited by Mike Fleetwood

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