shill: Merge mobile network operator databases.

Heretofore, we maintained two mobile network operator database files - one
derived from a former database format (serviceproviders.xml), and another
maintained by hand. Since we no longer track serviceproviders.xml, we can now
merge these two files. This will make it easier to maintain the database.

BUG=chromium:370194
TEST=- emerge platform2
     - Run network_3GSmokeTest.
CQ-DEPEND=CL:206054

Change-Id: I2b646636c487083497f0e119f37965d1ad3d829f
Reviewed-on: https://chromium-review.googlesource.com/206062
Tested-by: Prathmesh Prabhu <pprabhu@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Queue: Prathmesh Prabhu <pprabhu@chromium.org>