Signup: Deprecate the concept of reskinned flows.

[southp]

Details

The reskinned flow was introduced several years ago by the "Reskinned Signup Flow" project led by @niranjan-uma-shankar : pbxNRc-IO-p2. Now that it's basically the new default, we should deprecate that concept in code and make it the default behavior.

Checklist

• Deprecate isReskinned property, making the related behavior when it's true the default
• Deprecate the reskinned flow configuration, i.e. reskinned_flows in _shared.json
• Deprecate the overall usage of the terminology, e.g. in CSS and component names.

P2 discussions

• pdvytD-Yh-p2
• pdvytD-Yw-p2

Tasks

• Move all flows to non reskinned ui #98561
• Remove Is Reskinned Flag: Remove from user and notice sections #99112
• Remove Is Reskinned Flag: Untangle domain price of the isReskinned flag #99264
• Remove Is Reskinned Flag: Completely cleanup domains of the isReskinned flag #99440
• Remove Is Reskinned Flag: Remove isReskinned from all signup flows #99506
• Remove Is Reskinned Flag: Remove from user and notice sections - Attempt 2  #99354
• WPCC: Migrate wordpress connect flow to modern signup #98513
• Remove Is Reskinned Flag: Remove is reskinned from site selector #99572
• Remove Is Reskinned Flag: Final is reskinned cleanup #99690

[southp]

With the deployment of #99690, I believe we can close this now. Thanks for the amazing janitorial effort, @ddc22 :)