Drop default leaf definition and obsoleted comments

leaf is true by default. Other insns are not specifying it explicitly.
Also the comment describing why it was not leaf is outdated.

insns.def

@@ -1158,10 +1158,6 @@ opt_eq
 (CALL_INFO ci, CALL_CACHE cc)
 (VALUE recv, VALUE obj)
 (VALUE val)
-/* This instruction can compare a string with non-string.  This
- * (somewhat) coerces the non-string into a string, via a method
- * call. */
-// attr bool leaf = true;
 {
     val = opt_eq_func(recv, obj, ci, cc);
 
@@ -1176,8 +1172,6 @@ opt_neq
 (CALL_INFO ci_eq, CALL_CACHE cc_eq, CALL_INFO ci, CALL_CACHE cc)
 (VALUE recv, VALUE obj)
 (VALUE val)
-/* Same discussion as opt_eq. */
-// attr bool leaf = true;
 {
     val = vm_opt_neq(ci, cc, ci_eq, cc_eq, recv, obj);