Remove flavor config system

[guysoft]

Hey all,
To my knowloadge there is no one using the flavor build system, since you can just use the variant system.

Due to flag changes because of #151 I am alerting that I am planing to drop support for it.

If anyone has objections, is using it or has any other reason please object/support here.

[guysoft]

@mrbeam I can see this in your repos, are you still using it?

[guysoft]

Related mrbeam/BeamOS#90

[guysoft]

Got an answer from MR bean that they are using legacy CustomPiOS and don't mind. Also it seems like no one else is using it. Dropping support.

[kraeml]

May you have also to remove the paragraph in the wiki.

https://github.com/guysoft/CustomPiOS/wiki/Building#variant-flavors

[guysoft]

Thanks, done