ls-remote doc: fix example invocation on git.git

Under the EXAMPLES section, there is one invocation on the git.git
repository that attempts to list the refs master, pu, and rc.  The ref
rc does not exist in today's repository, so remove it.  Among other
things, this example demonstrates that the "<refs>..." argument is
simply a filter; requesting a non-existent ref is not an error.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
ls-remote doc: rewrite <repository> paragraph

Replace the <repository> paragraph containing specific references to
$GIT_DIR/branches and "." with a generic urls-or-remotes paragraph
referencing the relevant sections in the git-fetch(1) manpage.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
ls-remote doc: don't encourage use of branches-file

One outdated example encourages the use of $GIT_DIR/branches files.
Replace it with an equivalent example using a remote.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
t/t5505-remote: test multiple push/pull in remotes-file

Extend the test "migrate a remote from named file in $GIT_DIR/remotes"
to test that multiple "Push:" and "Pull:" lines in the remotes-file
works as expected.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
t/t5510-fetch: don't use remotes-file

Replace it with the equivalent gitconfig configuration, using the
results of a test in t/t5505-remote.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
t/t5515-fetch-merge-logic: don't use {branches,remotes}-file

Replace it with the equivalent gitconfig configuration, using the
results of the corresponding tests in t/t5505-remote.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
remote: deprecate read_{branches,remotes}_file

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>