[contactsd] Preserve existing behavior in removeBuddies

There was no need to alter the OfflineRosterBuffer behavior due to
failure of accountWrapper lookup.
[contactsd] Remove batch contact removal code

Performance of contact group removal is not very significant; simplify
the code by removing the unused, (presumably) optimized version.
[contactsd] Do not use NEMO_CONTACT_MANAGER env var to select contact engine

Contact manager engine selection is now controlled globally rather than
per-process.
[contactsd] Only retrieve the self contact ID once

The self contact ID cannot change.
[contactsd] Remove duplication in debug output code
[contactsd] Remove un-batched update code

Batched updates are preferable.
[contactsd] Remove sparql telepathy variant

Only QtMobility Contacts interface is now supported by telepathy interface
plugin.