Remove libcurl support from update_engine_sideload.

While sideloading an update from recovery we don't need nor want to
download payload from HTTP(S) URLs, only local file:// are supported.
This patch moves libcurl_http_fetcher and certificate_checker files out
of libpayload_consumer dropping the libcurl and libssl dependencies from
it and the update_engine_sideload.

Bug: 27178350
TEST=build UE for Brillo and Android. Unittests still pass and
update_engine_sideload doesn't link to libcurl.

Change-Id: Iffefdb094654f7277dc825c041fe55aac9ee8756