Remove a reference to optimize_diagonal.
Remove a reference to optimize_diagonal.

Commit 2dfcd899ad4 (February 2013) deprecated
SparsityPattern::optimize_diagonal() and it has since been removed from
the library.

jperryhouts/dealii,naliboff/dealii,angelrca/dealii,shakirbsm/dealii,EGP-CIG-REU/dealii,jperryhouts/dealii,sairajat/dealii,spco/dealii,EGP-CIG-REU/dealii,angelrca/dealii,sairajat/dealii,naliboff/dealii,danshapero/dealii,jperryhouts/dealii,danshapero/dealii,shakirbsm/dealii,kalj/dealii,kalj/dealii,JaeryunYim/dealii,angelrca/dealii,spco/dealii,pesser/dealii,kalj/dealii,danshapero/dealii,JaeryunYim/dealii,EGP-CIG-REU/dealii,naliboff/dealii,EGP-CIG-REU/dealii,jperryhouts/dealii,naliboff/dealii,angelrca/dealii,angelrca/dealii,pesser/dealii,jperryhouts/dealii,spco/dealii,sairajat/dealii,naliboff/dealii,kalj/dealii,EGP-CIG-REU/dealii,spco/dealii,danshapero/dealii,naliboff/dealii,JaeryunYim/dealii,kalj/dealii,spco/dealii,shakirbsm/dealii,spco/dealii,jperryhouts/dealii,jperryhouts/dealii,shakirbsm/dealii,JaeryunYim/dealii,danshapero/dealii,naliboff/dealii,spco/dealii,JaeryunYim/dealii,shakirbsm/dealii,danshapero/dealii,kalj/dealii,pesser/dealii,kalj/dealii,shakirbsm/dealii,pesser/dealii,pesser/dealii,EGP-CIG-REU/dealii,sairajat/dealii,angelrca/dealii,shakirbsm/dealii,sairajat/dealii,angelrca/dealii,EGP-CIG-REU/dealii,sairajat/dealii,JaeryunYim/dealii,pesser/dealii,sairajat/dealii,JaeryunYim/dealii,pesser/dealii,danshapero/dealii