clone: plug a miniscule leak
The remote_name variable is first assigned a copy of the value of
the "clone.defaultremotename" configuration variable and then by the
value of the "--origin" command line option. The former is prepared
to see multiple instances of the configuration variable by freeing
the current value of the variable before a copy of the newly
discovered value gets assigned to it. The latter however blindly
assigned a copy of the new value to the variable, thereby leaking
the value read from the configuration variable.
Signed-off-by: Junio C Hamano <gitster@pobox.com>