archiver.bbclass: Fix duplicated SRC_URIs for do_ar_original

The argument urls of bb.fetch2.Fetch(urls, d) are duplicated to SRC_URI, which caused errors like:

bb.data_smart.ExpansionError: Failure expanding variable SRCPV, expression was ${@bb.fetch2.get_srcrev(d)} which triggered exception FetchError: Fetcher failure: The SRCREV_FORMAT variable must be set when multiple SCMs are used.
The SCMs are:
git://github.com/docker/notary.git;destsuffix=git/src/github.com/docker/notary
git://github.com/docker/notary.git



The first one is from original SRC_URI, the second one is from the
variable 'urls', so cleanup SRC_URI before call bb.fetch2.Fetch() can fix the
problem.

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>