Removing files that now live in the {N}/docs repo. (#2937)

Previously, these files were automatically committed from this repo to the {N}/docs repo by a bot. That workflow confused people (mostly me), so the bot no longer does this. The canonical source of these files is now directly in the {N}/docs repo (specifically in https://github.com/NativeScript/docs/tree/master/plugins), so the files in this repo are no longer necessary.

Author: tjvantoll