Remove the unused bitcoind and lnd build contexts

Nothing references these now that the fixture pulls Polar's multi-arch
images instead of building locally. They could not produce a working image
anyway: the bitcoind Dockerfile is ubuntu:18.04 (EOL 2023) installing from
a PPA, and the lnd one builds from golang:1.11-alpine at a 2018 commit.

Leaving them would repeat the mistake that made the old setup misleading,
where plausible-looking files pointed at something that no longer worked.

docker/bitcoind/Dockerfile

@@ -1,10 +0,0 @@
-FROM ubuntu:18.04
-
-RUN apt-get -qq update && apt-get install -y software-properties-common
-
-RUN add-apt-repository -y ppa:bitcoin/bitcoin \
-  && add-apt-repository -y universe && apt-get update
-
-RUN apt-get install -y bitcoind
-
-ADD ./bitcoin.conf /bitcoin/bitcoin.conf

docker/bitcoind/bitcoin.conf

@@ -1,2 +0,0 @@
-daemon=0
-printtoconsole=1

docker/lnd/Dockerfile

@@ -1,29 +0,0 @@
-FROM golang:1.11-alpine as builder
-
-WORKDIR /go/src/github.com/lightningnetwork/lnd
-
-# Force Go to use the cgo based DNS resolver. This is required to ensure DNS
-# queries required to connect to linked containers succeed.
-ENV GODEBUG netdns=cgo
-
-RUN apk add --no-cache --update alpine-sdk git make \
-  && git clone -n https://github.com/lightningnetwork/lnd . \
-  && git checkout d2186cc9da29853091175189268b073f49586cf0 \
-  && make \
-  && make install
-
-# Start a new, final image to reduce size.
-FROM alpine as final
-
-# Expose lnd ports (server, rpc).
-EXPOSE 9735 10009
-
-# Copy the binaries and entrypoint from the builder image.
-COPY --from=builder /go/bin/lncli /bin/
-COPY --from=builder /go/bin/lnd /bin/
-
-# Add bash.
-RUN apk add --no-cache bash
-
-# Import the config
-ADD ./lnd.conf /root/.lnd/lnd.conf

docker/lnd/lnd.conf

@@ -1,2 +0,0 @@
-[Application Options]
-debuglevel=info