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

This reverts commit 60b70bb332d29fb5a2aecb801517be659cf4daf9.

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