chore: remove Lumo iconset from bundles

[sissbruecker]

Follow-up from https://github.com/vaadin/platform/pull/8068.

Removes the Lumo SVG iconset from the default bundles, as those should not contain theme specific code. The iconset will be loaded automatically when using the LumoIcon class, however it will require building a custom bundle.

Note that icons used by Vaadin components themselves will still be loaded by default as they are included as font icons within lumo.css.

[mshabarov]

We perhaps need a new Flow 25 alpha release to fix the validation as now platform code is running agains older Flow code that uses older Jackson.

[ZheSun88]

@mshabarov if the flow snapshot is ready, we can also update use flow snapshot version the versions.json. but i am afraid that the build will fail with the jackson incompatibility issue.

ah.. the failure is as in #8074

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