git-gui: reduce complexity of the quiet msgfmt rule

git-gui: reduce complexity of the quiet msgfmt rule

In non-verbose builds (without V=1) the rule to compile *.po files with
msgfmt captures the output in a shell variable and then strips down the
text produced by --statistics to fit on a 80 column line. The previous
commit removed --statistics output of the msgfmt invocation, so that we
don't get to see anything beyond "MSGFMT po/xx.msg" anymore. Make the
rule as minimal as the other "quiet" rules.

Signed-off-by: Johannes Sixt <j6t@kdbg.org>