Remove `simple_html_css`

[SlimShadyIAm]

The simple_html_css package caused build issues when using Flutter 3.22 because the Flutter team renamed some text styling properties the package used. Although this issue has been fixed in v5.0.0 of the package, it seems that the code that required simple_html_css is not called anywhere, so this package can be removed.

The alternative is upgrading the simple_html_css to 5.0.0, but then we need to make the research package use Flutter 3.22 as a minimum as well as any project that depends on it.

Closes #115

[albermoon]

Deleted the package and the widget which used the package are the best option if is unused and it didn't make sense to keep them in the project

[SlimShadyIAm]

As far as I can see, the removed InstructionText widget was previously used to render text within the RPUIInstructionStep:

https://github.com/cph-cachet/research.package/blob/5e7eedf4468f9c2de40669404ce090460c7cf92f/lib/src/ui/RPUIInstructionStep.dart#L59-L61

However, currently on master it is rendered using the Text widget:

https://github.com/cph-cachet/research.package/blob/f8dcd7968a3f0477a408bfd6c35448ab00ccf785/lib/src/ui/instruction_step.dart#L62-L66

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Similarly for the removed Title widget, when it was added:

https://github.com/cph-cachet/research.package/blob/5e7eedf4468f9c2de40669404ce090460c7cf92f/lib/src/ui/RPUIQuestionStep.dart#L89

vs. on master: https://github.com/cph-cachet/research.package/blob/f8dcd7968a3f0477a408bfd6c35448ab00ccf785/lib/src/ui/question_step.dart#L141-L145

[bardram]

However, currently on master it is rendered using the Text widget:

This makes sense - we can't translate HTML code so support for HTML can/should be removed.