[SSR] Remove hydration-related `data-lwc-*` attributes once hydration is complete

[ekashida]

We should remove the hydration-related data-lwc-* attributes once they've served their purpose to prevent users from taking a dependency on them.

[nolanlawson]

Specific steps: in hydration.ts, we look at a couple of special data-lwc-* attributes which instruct hydration to do certain things:

• data-lwc-host-mutated
• data-lwc-host-scope-token

These attributes should be removed from the element after they are read to avoid component authors taking a dependency on them (e.g. for styling with CSS selectors).