Makefile: don't invoke msgfmt with --statistics

Makefile: don't invoke msgfmt with --statistics

Remove the --statistics flag that I added in 5e9637c6297 (i18n: add
infrastructure for translating Git with gettext, 2011-11-18). Our
Makefile output is good about reducing verbosity by default, except in
this case:

    $ rm -rf po/build/locale/e*; time make -j $(nproc) all
        SUBDIR templates
        MKDIR -p po/build/locale/el/LC_MESSAGES
        MSGFMT po/build/locale/el/LC_MESSAGES/git.mo
        MKDIR -p po/build/locale/es/LC_MESSAGES
        MSGFMT po/build/locale/es/LC_MESSAGES/git.mo
    1038 translated messages, 3325 untranslated messages.
    5230 translated messages.

I didn't have any good reason for using --statistics at the time other
than ad-hoc eyeballing of the output. We don't need to spew out
exactly how many messages we've got translated every time. Now we'll
instead emit:

    $ rm -rf po/build/locale/e*; time make -j $(nproc) all
        SUBDIR templates
        MKDIR -p po/build/locale/el/LC_MESSAGES
        MSGFMT po/build/locale/el/LC_MESSAGES/git.mo
        MKDIR -p po/build/locale/es/LC_MESSAGES
        MSGFMT po/build/locale/es/LC_MESSAGES/git.mo

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>