Update GlIcon size in environments.vue

What does this MR do?

Closes #324796 (closed)

This MR has done as a part of https://gitlab.com/gitlab-com/marketing/community-relations/contributor-program/hackathon/-/issues/50

This MR remove the use-deprecated-sizes property in gl-icon component and update its size prop to use a valid size 16

Screenshots (strongly suggested)

Does this MR meet the acceptance criteria?

Conformity

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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
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Security

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Related to #324796 (closed)