Fix duplicated words in comment.

Reported-By: Peter Geoghegan
Discussion: https://postgr.es/m/CAH2-Wzn3rY2N0gTWndaApD113T+O8L6oz8cm7_F3P8y4awdoOg@mail.gmail.com
Backpatch: no, only present in master

src/backend/utils/sort/tuplesort.c

@@ -2102,9 +2102,9 @@ tuplesort_gettuple_common(Tuplesortstate *state, bool forward,
  * NULL value in leading attribute will set abbreviated value to zeroed
  * representation, which caller may rely on in abbreviated inequality check.
  *
- * If copy is true, the slot receives a copied tuple that'll that will stay
- * valid regardless of future manipulations of the tuplesort's state.  Memory
- * is owned by the caller.  If copy is false, the slot will just receive a
+ * If copy is true, the slot receives a copied tuple that will stay valid
+ * regardless of future manipulations of the tuplesort's state.  Memory is
+ * owned by the caller.  If copy is false, the slot will just receive a
  * pointer to a tuple held within the tuplesort, which is more efficient, but
  * only safe for callers that are prepared to have any subsequent manipulation
  * of the tuplesort's state invalidate slot contents.