Remove path_accelerationt interface

This interface only has a single implementation.

Author: tautschnig

src/goto-instrument/accelerate/path_acceleration.h

@@ -24,12 +24,11 @@ Author: Matt Lewis
 #include "polynomial.h"
 #include "path.h"
 #include "accelerator.h"
-#include "path_acceleration.h"
 #include "acceleration_utils.h"
 #include "cone_of_influence.h"
 #include "overflow_instrumenter.h"
 
-class polynomial_acceleratort:public path_accelerationt
+class polynomial_acceleratort
 {
 public:
   polynomial_acceleratort(