Revert "Add restrict keyword to pointers (not sharing the same memory for multiple fields)"

This reverts commit 60b70bb332.

It appears to have minimal performance impact, and fails to compile on
nvidia cards.

opencl_fdtd/simulation.py

@@ -169,7 +169,7 @@ class Simulation(object):
         ctype = type_to_C(self.arg_type)
 
         def ptr(arg: str) -> str:
-            return ctype + ' * restrict ' + arg
+            return ctype + ' *' + arg
 
         base_fields = OrderedDict()
         base_fields[ptr('E')] = self.E