Git.pm: remove redundant "use strict" from sub-package

Git.pm: remove redundant "use strict" from sub-package

In Perl the "use strict/warnings" pragmas are lexical, thus there's no
reason to do:

    package Foo;
    use strict;
    package Bar;
    use strict;
    $x = 5;

To satisfy the desire that the undeclared $x variable will be spotted
at compile-time. It's enough to include the first "use strict".

This functionally changes nothing, but makes a subsequent change where
"use warnings" will be added to Git.pm less confusing and less
verbose, since as with "strict" we'll only need to do that at the top
of the file.

Changes code initially added in a6065b548f ("Git.pm: Try to support
ActiveState output pipe", 2006-06-25).

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