Fix a typo in schur_eliminator.h

Change-Id: Ib2c6ea9598d49ee77e2f0429686045cf58cd8574

internal/ceres/schur_eliminator.h

diff --git a/internal/ceres/schur_eliminator.h b/internal/ceres/schur_eliminator.h
index 42c016e..45bb6c5 100644
--- a/internal/ceres/schur_eliminator.h
+++ b/internal/ceres/schur_eliminator.h
@@ -56,9 +56,8 @@
 // Where x = [y;z] is a partition of the variables.  The partitioning
 // of the variables is such that, E'E is a block diagonal matrix. Or
 // in other words, the parameter blocks in E form an independent set
-// of the of the graph implied by the block matrix A'A. Then, this
-// class provides the functionality to compute the Schur complement
-// system
+// of the graph implied by the block matrix A'A. Then, this class
+// provides the functionality to compute the Schur complement system
 //
 //   S z = r
 //