Remove isolation2 select for update case

There are two reasons that we can remove this case to
make pipeline a little faster:
  1. We have lock modes related cases, if lockmodes case passed,
     it should imply the select-for-update case is correct
  2. We have plan in future to enable isolation cases that test
     this.

src/test/isolation2/expected/select_for_update.out

-DROP TABLE IF EXISTS t;
-DROP
-
-CREATE TABLE t (c1 int, c2 int);
-CREATE
- INSERT INTO t values (1,1), (2,2), (3,3), (4,4);
-INSERT 4
-
-1: BEGIN;
-BEGIN
-2: BEGIN;
-BEGIN
-
-1: SELECT c2 FROM t WHERE c1 = 3 FOR UPDATE;
- c2 
-----
- 3  
-(1 row)
-2&: UPDATE t SET c2 = 999 where c1 = 3;  <waiting ...>
-
-1: END;
-END
-
-2<:  <... completed>
-UPDATE 1
-2: END;
-END
-
-1q: ... <quitting>
-2q: ... <quitting>
-
-DROP TABLE t;
-DROP

src/test/isolation2/isolation2_schedule

@@ -17,7 +17,6 @@ test: unlogged_appendonly_tables
 test: udf_exception_blocks_panic_scenarios
 
 # Tests on global deadlock detector
-test: select_for_update
 test: gdd/prepare
 test: gdd/dist-deadlock-01 gdd/dist-deadlock-04 gdd/dist-deadlock-05 gdd/dist-deadlock-06 gdd/dist-deadlock-07 gdd/dist-deadlock-102 gdd/dist-deadlock-103 gdd/dist-deadlock-104 gdd/dist-deadlock-106 gdd/non-lock-105
 # until we can improve below flaky case please keep it disabled

src/test/isolation2/sql/select_for_update.sql

-DROP TABLE IF EXISTS t;
-
-CREATE TABLE t (c1 int, c2 int);
- 
-INSERT INTO t values (1,1), (2,2), (3,3), (4,4);
-
-1: BEGIN;
-2: BEGIN;
-
-1: SELECT c2 FROM t WHERE c1 = 3 FOR UPDATE;
-2&: UPDATE t SET c2 = 999 where c1 = 3;
-
-1: END;
-
-2<:
-2: END;
-
-1q:
-2q:
-
-DROP TABLE t;