Remove grey0 and grey100 by replacing lightness0to100by2 -> lightness2to98by2

[lyzhan7]

Grey0 and grey100 are not specified in the updated designs for global color tokens. They are redundant with 'Black' and 'White'. Remove them by replacing lightness0to100by2 with lightness2to98by2.

Also tried to update any references I saw to lightness0to100by2 so that the documentation still made sense.

Testing:

• Followed instructions from https://microsoft.github.io/fluentui-token-pipeline/build.html
• Ran npm run build and npm run transform before this change and checked that build/react-native/tokens-global.json includes grey0/grey100, ran it after this change and confirmed that the file no longer contains grey0/grey100

[TravisSpomer]

Perfect! Thanks for updating the docs. I'll update the tokens repo after I publish this.