Here is another challenge in Julia. Imagine when have the following matrix:

```
 5.0  3.54924
 6.0  3.54702
 6.0  3.54655
 7.0  3.54168
 7.0  3.0

```

I want to delete the rows of the matrix for which the elements of the first column are duplicated. That will produce the following matrix, for example:

```
 5.0  3.54924
 6.0  3.54702
 7.0  3.0

```

Deletion of rows are arbitrary since we don't keep repeated values for the first column. How can I achieve that?