Change the API description for SparseCholesky::Solve.

The description does not reflect reality and puts constraints
on the underlying implementation.

Change-Id: I5f64e776c952868ae82fb2144acf51c2dcdfab56

internal/ceres/sparse_cholesky.h

diff --git a/internal/ceres/sparse_cholesky.h b/internal/ceres/sparse_cholesky.h
index 85487bf..96d2bfa 100644
--- a/internal/ceres/sparse_cholesky.h
+++ b/internal/ceres/sparse_cholesky.h
@@ -99,8 +99,6 @@
   // Computes the solution to the equation
   //
   // lhs * solution = rhs
-  //
-  // rhs and solution can point to the same memory location.
   virtual LinearSolverTerminationType Solve(const double* rhs,
                                             double* solution,
                                             std::string* message) = 0;