internal/registrytest: remove _registry remnants
A while ago we changed the registrytest so it didn't assume all
contents were in the `_registry` directory, but the package itself
still contained some logic related to that, so remove it.
Signed-off-by: Roger Peppe <rogpeppe@gmail.com>
Change-Id: I51374f92d913de2c70f255b13b67a3def03b8f98
Reviewed-on: https://review.gerrithub.io/c/cue-lang/cue/+/1171678
Unity-Result: CUE porcuepine <cue.porcuepine@gmail.com>
TryBot-Result: CUEcueckoo <cueckoo@cuelang.org>
Reviewed-by: Daniel Martí <mvdan@mvdan.cc>