Fix the incorrect credential access in SRPProvisionTrustCertChain.

Fix the incorrect credential access in SRPProvisionTrustCertChain.

SRPProvisionTrustCertChain deletes credential list.
But this credential list is read from global credential list through GetCredResourceDataByCredId API.
So credential list should not be deleted in SRPProvisionTrustCertChain.

Change-Id: I8c143d320ead4aea99daaa7d6882c11cfddf26e2
Signed-off-by: Chul Lee <chuls.lee@samsung.com>
Reviewed-on: https://gerrit.iotivity.org/gerrit/12377
Tested-by: jenkins-iotivity <jenkins-iotivity@opendaylight.org>
Reviewed-by: Greg Zaverucha <gregz@microsoft.com>
Reviewed-by: Randeep Singh <randeep.s@samsung.com>