Remove unnecessary overload for hash<>

The overload for pointers in hash tables was applied in normal
usage of schur_ordering.cc. However, the tests did not include the
overload since they only included collections_port.h. As a result,
the routines in schur_ordering.cc were using a different hash
function than that inside the tests.

The fix is to remove the specialization. If this breaks one of the
compiler configurations, we will find a workaround at that time.

Change-Id: Idbf60415d5e2aec0c865b514ad0c577d21b91405

internal/ceres/schur_ordering.cc

@@ -39,21 +39,6 @@
 #include "ceres/residual_block.h"
 #include "glog/logging.h"
 
-#if !defined(CERES_NO_TR1)
-
-CERES_HASH_NAMESPACE_START
-
-// Allow us to hash pointers as if they were int's
-template<> struct hash< ::ceres::internal::ParameterBlock*> {
-  size_t operator()(::ceres::internal::ParameterBlock* x) const {
-    return reinterpret_cast<size_t>(x);
-  }
-};
-
-CERES_HASH_NAMESPACE_END
-
-#endif
-
 namespace ceres {
 namespace internal {