[yugabyte#6511] YSQL: WARNING: 0A000: WITH clause not supported yet

Summary:
In yugabyte#6511, it was pointed out that in the following example:

```
with a as (
  select 1 as k)
delete from t
where k in (select k from a);
```

we throw the following warning:
```
WARNING:  0A000: WITH clause not supported yet
LINE 1: with a as (
        ^
HINT:  Please report the issue on https://github.com/YugaByte/yugabyte-db/issues
LOCATION:  raise_feature_not_supported_signal, gram.y:17327
```
However, we do support WITH clause, and this warning notwithstanding,
the delete does go through fine. As part of this change, removed this
warning message, and also imported PG tests for WITH clause.

The imported PG tests have the following major changes:
1) Temporary tables have been replaced by normal tables due to yugabyte#6783
2) Disabled the failing for test for updating a row more than once in different parts of a wCTE, will be handled separately in yugabyte#6782

Test Plan: ybd --scb --sj --java-test org.yb.pgsql.TestPgRegressWithClause

Reviewers: mihnea, neil

Reviewed By: neil

Subscribers: yql

Differential Revision: https://phabricator.dev.yugabyte.com/D10257

src/postgres/src/backend/parser/gram.y

@@ -11940,9 +11940,6 @@ DeleteStmt: opt_with_clause DELETE_P FROM relation_expr_opt_alias
 					n->whereClause = $6;
 					n->returningList = $7;
 					n->withClause = $1;
-					if (n->withClause != NULL) {
-						parser_ybc_not_support(@1, "WITH clause");
-					}
 					$$ = (Node *)n;
 				}
 		;