Remove too demanding test

Remove the test from commit 9c2e660b07.  This test ends up allocating
quite a bit of memory, which can make the test fail with out of memory
errors on some build farm machines.

src/test/regress/expected/prepare.out

@@ -184,11 +184,6 @@ SELECT name, statement, parameter_types, result_types FROM pg_prepared_statement
       |     UPDATE tenk1 SET stringu1 = $2 WHERE unique1 = $1;           |                                                    | 
 (6 rows)
 
--- max parameter number and one above
-PREPARE q9 AS SELECT $268435455, $268435456;
-ERROR:  there is no parameter $268435456
-LINE 1: PREPARE q9 AS SELECT $268435455, $268435456;
-                                         ^
 -- test DEALLOCATE ALL;
 DEALLOCATE ALL;
 SELECT name, statement, parameter_types FROM pg_prepared_statements

src/test/regress/sql/prepare.sql

@@ -78,9 +78,6 @@ PREPARE q8 AS
 SELECT name, statement, parameter_types, result_types FROM pg_prepared_statements
     ORDER BY name;
 
--- max parameter number and one above
-PREPARE q9 AS SELECT $268435455, $268435456;
-
 -- test DEALLOCATE ALL;
 DEALLOCATE ALL;
 SELECT name, statement, parameter_types FROM pg_prepared_statements