ldb: no need to call del_transaction in ldb_transaction_commit

ldb: no need to call del_transaction in ldb_transaction_commit

No matter commit succeeded or failed, transation will be delete afterwards.
So there is no need to delete it here.

Aganst Samba this causes an `LDAP error 51 LDAP_BUSY` error when the transaction
fails, say while we try to add users to groups in large amount and
the original error is lost.

In Samba, the rootdse module fails early in the del part of the
start/end/del pattern, and in ldb_tdb and ldb_mdb a failed commit
always ends the transaction, even on failure.

Signed-off-by: Joe Guo <joeg@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>