Remove support for custom edit activities

Test:
Tested the following editor scenarios:
  1) new contact
  2) edit other contact
  3) edit writable raw contact
  4) edit read-only raw contact (joins a new writable raw contact to it)
  5) edit aggregate w/ 1 writable and 1 read-only raw contact
  6) edit aggregate w/ 2 writable raw contacts
  7) edit local me raw contact
  8) edit local me raw contact joined with a read-only raw contact

Bug:31682268
Bug:31088704

Change-Id: I4000b4cef0d3c7beaa05cdef51ebdf978288c80f