Rename remote.uri to remote.url within remote handling internals

Rename remote.uri to remote.url within remote handling internals

Anyplace we talk about the address of a remote repository we always
refer to it as a URL, especially in the configuration file and
.git/remotes where we call it "remote.$n.url" or start the first
line with "URL:".  Calling this value a uri within the internal C
code just doesn't jive well with our commonly accepted terms.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>