Replace musicbrainz_unaccent with pgsql's unaccent extension

unaccent.sql

/**
 * MusicBrainz (http://musicbrainz.org) comes with a custom unaccent pgsql extension (musicbrainz_unaccent). 
 * However, AWS PGSQL service does not include this extension and it can not be easilly added. 
 *
 * The following code duplicates musicbrainz_unaccent functionality using the built in unaccent extension.
 */
CREATE EXTENSION unaccent;

CREATE OR REPLACE FUNCTION musicbrainz_unaccent(txt text) RETURNS text AS $$
BEGIN
    RETURN unaccent(txt);
END;
$$ LANGUAGE 'plpgsql' IMMUTABLE;

CREATE TEXT SEARCH DICTIONARY musicbrainz_unaccentdict (
    TEMPLATE = unaccent,
    RULES='unaccent'
);

/** 
 * Tests for the musicbrainz_unaccent extencion.
 * (The following code is not required to use the extension)
 */
SELECT musicbrainz_unaccent('Hôtel') = 'Hotel';
SELECT musicbrainz_unaccent('ľščťžýáí') = 'lsctzyai';
SELECT musicbrainz_unaccent('foo—bar‒baz') = 'foo—bar‒baz';
SELECT musicbrainz_unaccent('nonunicode') = 'nonunicode';
SELECT musicbrainz_unaccent('') = '';
SELECT musicbrainz_unaccent(null) IS NULL;
SELECT musicbrainz_unaccent(repeat('ä', 65536)) = repeat('a', 65536);
SELECT ts_lexize('musicbrainz_unaccentdict', 'ľščťžýáí foo—bar‒baz nonunicode') = E'{"lsctzyai foo—bar‒baz nonunicode"}’;