locator::ec2_multi_region_snitch: don't call for ec2_snitch::gossiper_starting()
locator::ec2_multi_region_snitch: don't call for ec2_snitch::gossiper_starting()

ec2_snitch::gossiper_starting() calls for the base class (default) method
that sets _gossip_started to TRUE and thereby prevents to following
reconnectable_snitch_helper registration.

Fixes #3454

Signed-off-by: Vlad Zolotarov <976c0f8d0852ed6439ad273880b400a75a7c41d0@scylladb.com>
Message-Id: <1528208520-28046-1-git-send-email-976c0f8d0852ed6439ad273880b400a75a7c41d0@scylladb.com>

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