neutralSecondaryAlt color removal final one!

[Vitalius1]

Bug Report

This is to track the removal of the remaining of usage of neutralSecondaryAlt color across the repo as continuation of #5194 and #6500.
I consider that this last issue should be the final cleanup and should be proceeded to only when we have answered the questions bellow.

Priorities and help requested:

Are you willing to submit a PR to fix? Yes

Requested priority: Normal

Describe the issue:

Here is where it can still be seen:

• fabric-website - should be as simple as confirming with designers on a replacement
• example-app-base - same as above
• experiments - most likely can be removed without breaking changes (it's experimental 😄 )
• styling - @phkuo can this be removed? I assume not as it will break downstream but can you confirm?
• office-ui-fabric-react - in here and here not sure if it needs to be left in this places. @phkuo do you have any context in here too?

[micahgodbolt]

@Vitalius1 any progress on this?

[phkuo]

It can be removed from the SASS variables (those weren't being exported until after the deprecation anyways), leave it in code where it is now for backwards compatibility.

[Vitalius1]

@phkuo I am a little bit confused on what do you mean by

...leave it in code where it is now...

Do you mean that anything in a .scss file can be removed and in cases of it being used in a .ts file should be left as is?

[phkuo]

I mean that it should be removed anywhere it is being consumed in Fabric components, but remain in place in the theming infrastructure code. i.e. deprecated but still technically supported

[Vitalius1]

#8098 is bringing back from deprecation neutralSecondaryAlt palette slot so this issue is no longer valid. Closing!