Remove the todo for smod.

It's not present in either WebAssembly or Rust, for example. We can
still add smod in the future if future use cases need it.

lib/cretonne/meta/base/instructions.py

@@ -782,11 +782,6 @@ srem = Instruction(
         Signed integer remainder. The result has the sign of the dividend.
 
         This operation traps if the divisor is zero.
-
-        .. todo:: Integer remainder vs modulus.
-
-            Should we add a ``smod`` instruction for the case where
-            the result has the same sign as the divisor?
         """,
         ins=(x, y), outs=a, can_trap=True)