Remove double wording in opaque type chapter
Fixes up some word soup I came across reading the chapter.
diff --git a/src/ffi.md b/src/ffi.md
index 2d60770..b4fdc02 100644
--- a/src/ffi.md
+++ b/src/ffi.md
@@ -912,8 +912,8 @@
we create an opaque type that we can't instantiate outside of this module.
(A struct with no field could be instantiated by anyone.)
We also want to use this type in FFI, so we have to add `#[repr(C)]`.
-The marker ensures the compiler does not mark the struct as `Send`, `Sync` and `Unpin` are
-not applied to the struct. (`*mut u8` is not `Send` or `Sync`, `PhantomPinned` is not `Unpin`)
+The marker ensures the compiler does not mark the struct as `Send`, `Sync`, and
+`Unpin`. (`*mut u8` is not `Send` or `Sync`, `PhantomPinned` is not `Unpin`)
But because our `Foo` and `Bar` types are
different, we’ll get type safety between the two of them, so we cannot
