Fix obsolete SQL syntax in comment.

This was legal back in the days of add_missing_from, though perhaps
never good style.  It's not legal anymore ...

Jan Urbański

src/backend/executor/execProcnode.c

@@ -32,6 +32,7 @@
  *		the number of employees in that department.  So we have the query:
  *
  *				select DEPT.no_emps, EMP.age
+ *				from DEPT, EMP
  *				where EMP.name = DEPT.mgr and
  *					  DEPT.name = "shoe"
  *