从数组中删除重复的键？

Question

I have the following array:

Array
(
    [https://i.imgur.com/UYK4Agz.png] => dummy2
    [https://i.imgur.com/UYK4Agz.png] => dummy2
    [https://i.imgur.com/vyGHgZN.jpg] => dummy2
    [https://i.imgur.com/vyGHgZN.jpg] => dummy1
)

Id like to remove all duplicate keys. This is the expected result:

Array
(
    [https://i.imgur.com/UYK4Agz.png] => dummy2
    [https://i.imgur.com/vyGHgZN.jpg] => dummy2
)

Tried using array_unique but it only works for values.

Also took a look at other posts here but they all talk about way bigger arrays, im really confused.

Sorry for the noobish question, please point me to the right function I should use!

Thanks SO xx