Rename LinearSolverTerminationType enums.

This increases clarity, drops redundant enums and makes things
cleaner all around.

Change-Id: I761f195ddf17ea6bd8e4e55bf5a72863660c4c3b
diff --git a/internal/ceres/trust_region_strategy.h b/internal/ceres/trust_region_strategy.h
index 3f078d5..998514f 100644
--- a/internal/ceres/trust_region_strategy.h
+++ b/internal/ceres/trust_region_strategy.h
@@ -106,7 +106,7 @@
     Summary()
         : residual_norm(0.0),
           num_iterations(-1),
-          termination_type(FAILURE) {
+          termination_type(LINEAR_SOLVER_FAILURE) {
     }
 
     // If the trust region problem is,