pgsql: Remove read_file/write_file tests.

Log Message:
-----------
Remove read_file/write_file tests. These were originally intended to
*fail*, to test that plpython didn't allow untrusted operations.
When we changed plpython to plpythonu because python didn't actually have
a secure sandbox mode, someone (probably me :-() misinterpreted the tests
as checking whether Python's file I/O works. Which is a stupid thing for
us to be testing. Remove it so we don't clutter the filesystem with
random temporary files.

Modified Files:
--------------
pgsql/src/pl/plpython/expected:
plpython_error.out (r1.1 -> r1.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_error.out.diff?r1=1.1&r2=1.2)
plpython_function.out (r1.1 -> r1.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/expected/plpython_function.out.diff?r1=1.1&r2=1.2)
pgsql/src/pl/plpython/sql:
plpython_error.sql (r1.1 -> r1.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_error.sql.diff?r1=1.1&r2=1.2)
plpython_function.sql (r1.1 -> r1.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/pl/plpython/sql/plpython_function.sql.diff?r1=1.1&r2=1.2)