Remove redundant NULL checks before free()/delete (#2184)

Remove redundant NULL checks before free()/delete

The ISO C and C++ standards guarantee that it's safe to call these
on a NULL pointer, so it's not necessary for the calling code to
also check.

Fixes https://sourceforge.net/p/swig/feature-requests/70/

Lib/d/cpointer.i

@@ -54,14 +54,14 @@ NAME() {
   return new TYPE();
 }
 ~NAME() {
-  if (self) delete self;
+  delete self;
 }
 #else
 NAME() {
   return (TYPE *) calloc(1,sizeof(TYPE));
 }
 ~NAME() {
-  if (self) free(self);
+  free(self);
 }
 #endif
 }
@@ -133,9 +133,9 @@ static TYPE *copy_##NAME(TYPE value) { %}
 
 static void delete_##NAME(TYPE *self) { %}
 #ifdef __cplusplus
-%{  if (self) delete self; %}
+%{  delete self; %}
 #else
-%{  if (self) free(self); %}
+%{  free(self); %}
 #endif
 %{}