[Qt] Optimize properties in about_dialog

[sampletext32]

fixes #8225

What this PR does

1. Removes keyboard interaction with labels, so multiple cursors doesn't appear.
2. Removes double-include resources in about dialog.ui.
3. Removes some flags as they are in a more general one.

[Megamouse]

you are not fixing anything by removing functionality.
This rather looks like some strange Qt bug instead of our problem

[sampletext32]

As was said in issue, text selection behavior is likely undesired and unnecessary in this window. So removing is the thing.
I don't think users really need to copy any of that texts.

All editable or at least selectable texts should be in an EditText control. These are Labels, which usually serves to display texts, but not allow any kind of edit/select.

And it's fixed the issue btw.

[sampletext32]

Oh, and welcome_dialog displays the same header, but doesn't allow text selection, so this is another argument to disable it in about_dialog

[sampletext32]

Wait a bit, I will run a small test.

[sampletext32]

I've looked through documentation
https://doc.qt.io/qt-5/qt.html#TextInteractionFlag-enum
and found out that only selectableByKeyboard produces cursors.

[sampletext32]

Found a solution - text can be selected, but cursors doesn't appear.

[Megamouse]

If this works then it is much better. In case you were wondering: Text was made selectable to fix a prior issue, so it was indeed intended.