Fix depreciated GLIcon size and property

What does this MR do and why?

This MR removes the use-deprecated-sizes property in gl-icon component and update its size prop to use a valid size in ee/app/assets/javascripts/subscriptions/new/components/order_summary.vue

Closes - #324792 (closed)

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Screen_Recording_2021-10-19_at_18.28.48

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