http: drop "local" member from request struct

http: drop "local" member from request struct

This is a FILE pointer in the case that we are sending our
output to a file. We originally used it to run ftell() to
determine whether data had been written to our file during
our last call to curl. However, as of the last patch, we no
longer care about that flag anymore. All uses of this struct
member are now just book-keeping that can go away.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>