[web] deprecate and clean up unused tabs code

Summary:
Now that all the use cases of the tabs component has been updated to use the new tabs component api, we can deprecate our legacy tabs component. Also in this diff took a moment to update the color variables for the tabs style to use the new color design system naming convention

Depends on D10523

Test Plan: flow + confirmed that the tabs had no visual regression

Reviewers: atul, inka

Reviewed By: atul

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D10524