[algorithm.syn] Remove stray comma.

This seems to be an error in the wording of LWG 4544 (LWG Motion 2).

Addresses editorial review committee feedback.

Author: tkoeppe

source/algorithms.tex

@@ -3633,7 +3633,7 @@
   namespace ranges {
     template<class I, class O>
       using @\libglobal{set_difference_result}@ = in_out_result<I, O>;
-    template<class I1, class, I2, class O>
+    template<class I1, class I2, class O>
       using @\libglobal{set_difference_truncated_result}@ = in_in_out_result<I1, I2, O>;
 
     template<@\libconcept{input_iterator}@ I1, @\libconcept{sentinel_for}@<I1> S1, @\libconcept{input_iterator}@ I2, @\libconcept{sentinel_for}@<I2> S2,