Update component registration logic

[sun-mota]

Please verify the version of auro-flight you have installed

No response

Please describe the bug

Default import of index.js should register the default custom element only.

import of the component class should not register the custom element at all.

Remove all registration of custom-${component name} from the JS and only register as part of ./demo/index.js

Reproducing the error on the docsite

None

Expected behavior

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What browsers are you seeing the problem on?

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Additional context

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Exit criteria

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