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 5f92da62c686c12c00fc9f7948654816c586f838.

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

This reverts commit eeeb0888d437ac0147cfe4b81aba264cf0d00b70.

Revert "Add apns/eri for Boost Mobile"

This reverts commit b207e2eda31e10a45a20774c61dc350975095d1b.

Revert "add more vzw eri's"

This reverts commit 82e10af192daaacf9e819253264a09a7051d0e06.

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

This reverts commit 1af75f1ba7abb351ec1113eeceaa00389a119e3b.

Revert "Multi-carrier overlays: Fix Mms"

This reverts commit f8b0737a435d211b01baf5df3feb9f98039884e2.

Revert "Generic multi-carrier overlays based on hammerhead"

This reverts commit 6f5758c9c33d1be82f76e32a8d83b427204436d1.

Change-Id: I3495a89ce405362dc558f7ec7f0e61adea9fa507