builtin/ls-remote: fix leaking `pattern` strings

builtin/ls-remote: fix leaking `pattern` strings

Users can pass patterns to git-ls-remote(1), which allows them to filter
the list of printed references. We assemble those patterns into an array
and prefix them with "*/", but never free either the array nor the
allocated strings.

Refactor the code to use a `struct strvec` instead of manually tracking
the strings in an array. Like this, we can easily use `strvec_clear()`
to release both the vector and the contained string for us, plugging the
leak.

Helped-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>