[FIX] web,mrp_subcontracting: list: remove width attribute for button

Before this commit, the `width` attribute was interpreted by a jQuery node generator
function as a `style="width"` property and gave an incorrect width value to the affected node.

Now, the `width` attribute is automatically plucked in the list renderer in the
specific function used to render buttons.

Task 2076721

X-original-commit: c67b36c0