Deprecate Base64 Encoding API

[ActualMasterOogway]

Deprecate base64decode and base64encode in favour of EncodingService:Base64Decode and EncodingService:Base64Encode. Roblox's newly added EncodingService covers Base64 De/Encoding and therefore custom functions for those are useless.

[ActualMasterOogway]

EncodingService is currently locked behind a Fast Flag which is disabled by default as of now

[Richy-Z]

We already have this deprecation planned for the next release of sUNC, but thank you for the reminder. 👍