Remove duplicate methods of WoltModalSheet

[ulusoyca]

Description

We introduced static in-modal navigation methods to WoltModalSheet but not released (#188). After receiving feedback #202 (comment) I agree that there are two ways of using the same method. This PR utilizes only WoltModalSheet.of(context).method type of methods for in-modal navigation.

Related Issues

Fixes #202 (comment)

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• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes tests for all changed/updated/fixed behaviors.
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• I updated/added relevant documentation (doc comments with ///).
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Breaking Change

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• Yes, this is a breaking change.
• No, this is not a breaking change.

[github-actions]

Visit the preview URL for this PR (updated for commit 2bd1f60):

• https://coffeemakerexample--pr208-remove-unnecessary-d-o1zk5ifo.web.app
• https://playgroundwoltexample--pr208-remove-unnecessary-d-dyo6rlw4.web.app
• https://playgroundnavigator2woltexample--pr208-remove-unnecess-he9wdbkc.web.app

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