Remove no-longer-used ifdef

This is no longer necessary as of 2db625a.

Author: tautschnig

src/goto-instrument/full_slicer.cpp

@@ -14,8 +14,6 @@ Author: Daniel Kroening, [email protected]
 
 #include <util/find_symbols.h>
 #include <util/cprover_prefix.h>
-#ifdef DEBUG_FULL_SLICERT
-#endif
 
 #include <goto-programs/remove_skip.h>