Remove LogCallback in ts definition files

[tokidoki11]

Background

LogCallback is not supported anymore as per version 3 and can cause confusion

https://github.com/winstonjs/winston/blob/HEAD/UPGRADE-3.0.md#winstonlogger
winston.Logger.log and level-specific methods (.info, .error, etc) no longer accepts a callback.

This PR removes the LogCallback types and its reference in LogLevelMethod and LogMethod interface

closes: #1922

[DABH]

These changes seem fine per the issue linked in the PR description, but see the discussion in that issue - need to figure out if this goes in a major or minor release. A bit hesitant to do a major release for some TS changes, but perhaps it's ok to do this as a minor release if these TS definitions never worked?