mysql> DROP INDEX `post_text` ON phpbb_posts;
Query OK, 251171 rows affected (7 min 35.04 sec)
Records: 251171  Duplicates: 0  Warnings: 0

mysql> ALTER TABLE phpbb_posts DROP INDEX `post_content`;
Query OK, 251182 rows affected (1 min 45.06 sec)
Records: 251182  Duplicates: 0  Warnings: 0

mysql> ALTER TABLE phpbb_posts DROP INDEX `post_subject`;
Query OK, 251188 rows affected (1 min 32.55 sec)
Records: 251188  Duplicates: 0  Warnings: 0

CREATE TABLE phpbb_posts_new LIKE phpbb_posts;
ALTER TABLE phpbb_posts_new DROP INDEX post_text;
ALTER TABLE phpbb_posts_new DISABLE KEYS;
INSERT INTO phpbb_posts_new SELECT * FROM phpbb_posts;
ALTER TABLE phpbb_posts_new ENABLE KEYS;
ALTER TABLE phpbb_posts RENAME phpbb_posts_old;
ALTER TABLE phpbb_posts_new RENAME phpbb_posts;
DROP TABLE phpbb_posts_old;