Remove redundant lines from partition_ddl test

Spotted when analyzing a CI failure pertaining to another test.

Reviewed by Heikki and Georgios.

src/test/regress/input/partition_ddl.source

@@ -601,18 +601,9 @@ END (date '2009-03-01') EXCLUSIVE
 SUBPARTITION asia VALUES ('asia'),
 SUBPARTITION europe VALUES ('europe') );
 
-ALTER TABLE mpp3377_sales ADD PARTITION
-START (date '2009-02-01') INCLUSIVE
-END (date '2009-03-01') EXCLUSIVE
-( SUBPARTITION usa VALUES ('usa'),
-SUBPARTITION asia VALUES ('asia'),
-SUBPARTITION europe VALUES ('europe') );
-
 -- This is the new way
 ALTER TABLE mpp3377_sales ADD PARTITION START (date '2009-02-01') INCLUSIVE END (date '2009-03-01') EXCLUSIVE;
 
-ALTER TABLE mpp3377_sales ADD PARTITION START (date '2009-02-01') INCLUSIVE END (date '2009-03-01') EXCLUSIVE;
-
 CREATE TABLE mpp3250 (
         unique1         int4,
         unique2         int4,

src/test/regress/output/partition_ddl.source

@@ -2280,17 +2280,8 @@ END (date '2009-03-01') EXCLUSIVE
 SUBPARTITION asia VALUES ('asia'),
 SUBPARTITION europe VALUES ('europe') );
 ERROR:  subpartition configuration conflicts with subpartition template
-ALTER TABLE mpp3377_sales ADD PARTITION
-START (date '2009-02-01') INCLUSIVE
-END (date '2009-03-01') EXCLUSIVE
-( SUBPARTITION usa VALUES ('usa'),
-SUBPARTITION asia VALUES ('asia'),
-SUBPARTITION europe VALUES ('europe') );
-ERROR:  subpartition configuration conflicts with subpartition template
 -- This is the new way
 ALTER TABLE mpp3377_sales ADD PARTITION START (date '2009-02-01') INCLUSIVE END (date '2009-03-01') EXCLUSIVE;
-ALTER TABLE mpp3377_sales ADD PARTITION START (date '2009-02-01') INCLUSIVE END (date '2009-03-01') EXCLUSIVE;
-ERROR:  new partition overlaps existing partition
 CREATE TABLE mpp3250 (
         unique1         int4,
         unique2         int4,