Drop enforcing async import of ee_components

What does this MR do and why?

Remove the enforcement for async imports of ee_component alias from the FE guide docs.

We already have examples of sync imports in CE codebase (e.g. merge_request.vue), and FOSS (and relevant pipelines) seem to work just fine with that import.

We don't enforce async imports on the ee_else_ce and similar aliases, and they are defined in pretty-much the same way in the webpack.config.js.

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