Remove unused development mode in ayon setting

[moonyuet]

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Description

Quoted from @antirotor

originally, dev mode was introduced in OpenPype in ages of Unreal 4.26 when Unreal didn't really have python api, so you actually needed visual studio and everything else to make it work. Nowdays, I don't think dev mode is actually used at all. There are some obscure cases for needing C++ style project - for example when you need to build Deadline plugins for Unreal, etc. 

We can remove the dev mode in ayon settings as Unreal have more mature support on python API. We dont really need that anymore for the development of the integration.

Steps To Reproduce:

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Additional context:

Version

ayon_unreal: 0.2.9

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