[2.0] generally remove all code marked as "deprecated" (front end)

[rusackas]

Look for comments stating that things that will be removed for, and remove them

[graceguo-supercat]

@eschutho and I went through superset-frontend code base and found 2 deprecation candidates:

• superset/superset-frontend/packages/superset-ui-core/src/time-format/TimeFormatterRegistrySingleton.ts

  Line 78 in e632193

  * TODO: Deprecate this in the next breaking change.

  
  in use by "OMNIBAR" feature

• superset/superset-frontend/src/components/OmniContainer/Omnibar.tsx

  Line 30 in e6ef7da

  * @deprecated Component "omnibar" does not support prop className or id (the original implementation used className). However, the original javascript code was sending these prop and was working correctly. lol

  
  in use by table, pivot table, big number visualization.

But both of them are currently in use and no replacement code available. So we think it's not a right time to deprecate them right now.

[rusackas]

Sweep through and change any comments like "will be deprecated in 2.0" to be "will be deprecated in a future version"

[rusackas]

Consider removing Omnibar for 3.0 - @suddjian we should start 3.0 proposals board

[graceguo-supercat]

Given this discussion: #13305 (comment), we should consider remove this feature (now or 3.0)

[rusackas]

I believe that since it was already marked as deprecated in the code, it's fair game to remove as part of this initiative. That work could be part of this Issue, or filed a separate one if need be, but I have no objection to the removal as part of 2.0.