internal/golangorgx/vendoring: remove

I forgot to remove this alongside the revendoring script
in https://cuelang.org/cl/1218308.

Signed-off-by: Daniel Martí <[email protected]>
Change-Id: Ic54e1602481323e21c3421f1f81e85b2bca76a4a
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1218453
Unity-Result: CUE porcuepine <[email protected]>
TryBot-Result: CUEcueckoo <[email protected]>
Reviewed-by: Matthew Sackman <[email protected]>

Author: mvdan