SurfaceFlinger: Removed createScopedConnection.

Scoped connections existed to constrain clients to only making
surfaces with parents. However now that we support off-screen parents
this is no longer required and we can use normal connections everywhere.
We take however care that only priviledged clients can place layers
in the current state.

Test: Manual
Bug: 62536731
Bug: 111373437
Bug: 111297488
Change-Id: I0a034767e92becec63071d7b1e3e71b95d505b77