shill: De-duplicate MTS entry in mobile operator database.

MTS was included in both |additional_providers| and |serviceproviders|. This CL
merges the two entries together.

BUG=chromium:278151
TEST=(1) emerge-falco shill
     (2) Test that MTS name shows up correctly on the MTS network.

Change-Id: Ie17f8efe0667679147c8e14a48aa3f2dfd9ddac9
Reviewed-on: https://chromium-review.googlesource.com/204717
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Prathmesh Prabhu <pprabhu@chromium.org>
Tested-by: Prathmesh Prabhu <pprabhu@chromium.org>