Squashed revert of mms and spn-specific overlays

In theory, could have been a good idea, but ultimately just leads to
headaches for device maintainers that need to overlay any of these.

Revert "overlay: remove Verizon specific eri.xml"

This reverts commit 5f92da62.

Revert "Add Japanese APNs/eri for au, docomo MVNO, EMOBILE and SoftBank"

This reverts commit eeeb0888.

Revert "Add apns/eri for Boost Mobile"

This reverts commit b207e2ed.

Revert "add more vzw eri's"

This reverts commit 82e10af1.

Revert "multi-carrier overlays: Add eri and config for US Cellular"

This reverts commit 1af75f1b.

Revert "Multi-carrier overlays: Fix Mms"

This reverts commit f8b0737a.

Revert "Generic multi-carrier overlays based on hammerhead"

This reverts commit 6f5758c9.

Change-Id: I3495a89ce405362dc558f7ec7f0e61adea9fa507