WIP: Merge T6UL

Change-Id: Idc41f0ab1925d3ec4cc8be49367ddcdcc2453123
m7-common: update mms overlays

frameworks/base - default config.xml:
- Remove content disposition override which should be limited to Sprint.

mcc311/mnc480:
- Remove overlays which duplicate the default configuration.
- Remove overrides for defaultMMSMessagesPerThread and
  defaultSMSMessagesPerThread.

mcc310mnc120:
- Remove overlays which duplicate the default configuration.
- Remove overrides for defaultMMSMessagesPerThread and
  defaultSMSMessagesPerThread.
- Remove enableSprintVVM which seems to no longer be used.

Change-Id: I6d8f089856c377b40752019f751cbd5cd64344d3