morphisms: remove 'return 0;' at end since it is now added by default

morphisms/uint.morphism-base

@@ -0,0 +1,17 @@
+```
+```
+
+morph_nat_as_u8_to_u16 ()
+      ℕ ~ native.UInt8
+-->   ℕ ~ native.UInt16
+```*dst = *src;```
+
+morph_nat_as_u16_to_u32 ()
+      ℕ ~ native.UInt16
+-->   ℕ ~ native.UInt32
+```*dst = *src;```
+
+morph_nat_as_u32_to_u64 ()
+      ℕ ~ native.UInt32
+-->   ℕ ~ native.UInt64
+```*dst = *src;```