Remove spurious word.

Tatsuo Ishii

doc/src/sgml/parallel.sgml

@@ -241,7 +241,7 @@ EXPLAIN SELECT * FROM pgbench_accounts WHERE filler LIKE '%x%';
     than normal but would produce incorrect results.  Instead, the parallel
     portion of the plan must be what is known internally to the query
     optimizer as a <firstterm>partial plan</>; that is, it must constructed
-    so that each process will which executes the plan will generate only a
+    so that each process which executes the plan will generate only a
     subset of the output rows in such a way that each required output row
     is guaranteed to be generated by exactly one of the cooperating processes.
   </para>