I think some of the confusion may lie in realizing what exactly it means to "subscribe" to a magazine on EYB -- if you have elected to "subscribe" to say Food & Wine on EYB, you were given the option to automatically add future issues of that magazine to your EYB bookshelf and also to add past issues for a specific time period -- so say I have every issue for the past 2 years, I would plug in the dates and then they would have been added all at once, eliminating the need for me to page through the library and add each issue individually.
If you had selected 'Automatically add future editions to my Bookshelf,' only then will the option to "remove" be listed underneath the magazine's cover and the header "Subscribe to this magazine". If you have not subscribed, there is only a "Subscribe" button -- if you were to click on that, it gives you the options I described above. Whether or not you are subscribed to a magazine on EYB, if you wish to remove issues already on your shelf, you need to remove them manually because unsubscribing on EYB only stops future issues from being added to your shelf, it does not affect issues already on your shelf.
So if you are trying to remove all the Australian Gourmet Traveller issues from your shelf, the easiest way I can recommend is to search for "Australian Gourmet Traveller" on the magazine tab of your bookshelf and then click on the condensed view (shown in the image below) which shows up to 200 issues per page of search results. Then you can just click on the "x"s all the way down the page on the right-hand side and quickly delete them all.

That's probably more information than you were even looking for, but I hope it helps clear things up!