Remove duplicate unique index for wordlist table

[BlackbitDevs]

The UNIQUE index for wordlist.term gets created in

tntsearch/src/Engines/MysqlEngine.php

Line 38 in 069e63e

$this->index->exec("ALTER TABLE ".$this->indexName."_wordlist ADD UNIQUE INDEX unique_term (`term`);");

and in

tntsearch/src/Engines/MysqlEngine.php

Line 33 in 781e0ee

term VARCHAR(255) UNIQUE,

One of the 2 places can be removed.
This PR removed the latter one.