quote_path_relative(): remove redundant parameter

quote_path_relative(): remove redundant parameter

quote_path_relative() used to take a counted string as its parameter
(the string to be quoted).  With an earlier change, it now uses
relative_path() that does not take a counted string, and we have
been passing only the pointer to the string since then.

Remove the length parameter from quote_path_relative() to show that
this parameter was redundant.  All the changed lines show that the
caller passed either -1 (to ask the function run strlen() on the
string), or the length of the string, so the earlier conversion was
safe.

All the callers of quote_path_relative() that used to take counted string
have been audited to make sure that they are passing length of the actual
string (or -1 to ask the callee run strlen())

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>