t5501-*.sh: Fix url passed to clone in setup test

t5501-*.sh: Fix url passed to clone in setup test

In particular, the url passed to git-clone has an extra '/' given
after the 'file://' schema prefix, thus:

    git clone --reference=original "file:///$(pwd)/original one

Once the prefix is removed, the remainder of the url looks something
like "//home/ramsay/git/t/...", which is then interpreted as an
network path. This then results in a "Permission denied" error, like
so:

    ramsay $ ls //home
    ls: cannot access //home: No such host or network path
    ramsay $ ls //home/ramsay
    ls: cannot access //home/ramsay: Permission denied
    ramsay $

In order to fix the problem, we simply remove the extraneous '/'
character from the url.

Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>