dsdb: Split rename case out of replmd_op_possible_conflict_callback

dsdb: Split rename case out of replmd_op_possible_conflict_callback

This avoids running this code path, originally written for the add case, in
a semi-async manner in the rename case, which caused both bugs and complexity.

This does create a deal of duplicated code, but it is easier to follow because
there are no longer special cases for ADD and RENAME in the "common" code and
the behaviour of ldb_module_done() and the callbacks is well defined and expected

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Garming Sam <garming@catalyst.net.nz