Dialer: Remove compatibility (1/x)

* Now that we don't expect any more changes we can rip out
  all the unused stuff
* Start with all the TargetApi-checks for N, O and P including
  version checks in code for those and remove the old number
  blocking - we have the provider since 2017 now...

Change-Id: Ib9369476fa660c44d946b0e41b0d23a34ff14e7c