Add the 2_d_d SchurEliminator specialization.

This occurs far too often in bundle adjustment problems to be ignored.

Change-Id: Ib137f1566acf5fffa63e50a55fe8e78ea9eb1c14
diff --git a/internal/ceres/generate_eliminator_specialization.py b/internal/ceres/generate_eliminator_specialization.py
index caeca69..78f779f 100644
--- a/internal/ceres/generate_eliminator_specialization.py
+++ b/internal/ceres/generate_eliminator_specialization.py
@@ -60,6 +60,7 @@
                    (2, 4, 3),
                    (2, 4, 4),
                    (2, 4, "Eigen::Dynamic"),
+                   (2, "Eigen::Dynamic", "Eigen::Dynamic"),
                    (4, 4, 2),
                    (4, 4, 3),
                    (4, 4, 4),