Fix return type error when re-defining get_constraints_for_table SQL function

[seancolsen]

The msar.get_constraints_for_table SQL function had previously been defined with a different return type. That meant that restarting the service layer would give:

------------Setting up User Databases------------
Installing Mathesar on preexisting PostgreSQL database mathesar at host mathesar_dev_db...
Traceback (most recent call last):
  File "/usr/local/lib/python3.9/runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/usr/local/lib/python3.9/runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "/code/mathesar/install.py", line 61, in <module>
    main()
  File "/code/mathesar/install.py", line 37, in main
    install_on_db_with_key(database_key, skip_confirm)
  File "/code/mathesar/install.py", line 46, in install_on_db_with_key
    install.install_mathesar(
  File "/code/db/install.py", line 31, in install_mathesar
    sql_install.install(user_db_engine)
  File "/code/db/sql/install.py", line 13, in install
    load_file_with_engine(engine, file_handle)
  File "/code/db/connection.py", line 79, in load_file_with_engine
    conn.execute(file_handle.read())
  File "/usr/local/lib/python3.9/site-packages/psycopg/connection.py", line 891, in execute
    raise ex.with_traceback(None)
psycopg.errors.InvalidFunctionDefinition: cannot change return type of existing function
DETAIL:  Row type defined by OUT parameters is different.
HINT:  Use DROP FUNCTION msar.get_constraints_for_table(oid) first.

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[mathemancer]

LGTM