dbal conventions: remove buggy optimization

Having different primary keys in referencing tables does not mean
that they will be named the same in the joining table. Use proper
heuristic for PK resolution.

src/Mapper/Dbal/Conventions/Conventions.php

@@ -264,12 +264,6 @@ public function getManyHasManyStorageName(IConventions $targetConventions): stri
 
 	public function getManyHasManyStoragePrimaryKeys(IConventions $targetConventions): array
 	{
-		$one = $this->getStoragePrimaryKey()[0];
-		$two = $targetConventions->getStoragePrimaryKey()[0];
-		if ($one !== $two) {
-			return [$one, $two];
-		}
-
 		return $this->findManyHasManyPrimaryColumns(
 			$this->getManyHasManyStorageName($targetConventions),
 			$targetConventions->getStorageTable()