remove Either, Left, and Right from syntax files

[bytbox]

Changes only to src/etc.

[huonw]

Hm, this PR is confused.

@bytbox it looks like you are working off your master branch for both the removal of do & the (original) contents of this PR, and so the removal of Either never actually landed since you possibly force-pushed do over the top.

In general, I recommend using branches and just keep master as strictly tracing the master branch of the main repository. Feel free to restore the Either removal for a new r+ here, or close this one and open a new PR with a non-master branch.

(Random example of "feature branch" usage of git.)

[bytbox]

Oh, I done goofed... ok, I think I can fix this elegantly.

[bytbox]

I think I got it right. I'll use separate branches for all future changes; thanks.

[huonw]

Awesome! :)