Revert "Icons: maintain absolute stroke-width regardless of icon-size (#78774)"

[t-hamano]

What?

This reverts commit 86c5139 (#78774).

Why?

We applied an approach that maintains an absolute stroke width regardless of icon size to the square icon. However, this icon caused unintended changes in the editor. The cause is the following CSS.

.components-button svg {
    fill: currentColor;
}

Let's revert #78774 and explore a more ideal approach in #78808.

How?

Testing Instructions

Check the Zoom out button.

Screenshots or screencast

Before	After

Use of AI Tools

None

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Co-authored-by: t-hamano <wildworks@git.wordpress.org>
Co-authored-by: jasmussen <joen@git.wordpress.org>

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[jasmussen]

I very much appreciate all your help with this work!