Simplify github action build

.github/workflows/docker.yml

@@ -9,9 +9,6 @@ jobs:
   docker:
     runs-on: ubuntu-latest
     steps:
-      -
-        name: Set up QEMU
-        uses: docker/setup-qemu-action@v1
       -
         name: Set up Docker Buildx
         uses: docker/setup-buildx-action@v1

Dockerfile

@@ -5,14 +5,6 @@ WORKDIR /bot
 
 RUN apt-get update && apt-get install -y cmake && apt-get clean
 
-# This is a dummy build to get the dependencies cached.
-COPY Cargo.toml Cargo.lock ./
-RUN mkdir src && \
-    echo "// dummy file" > src/lib.rs && \
-    cargo build --release && \
-    rm -r src
-
-# This is the actual build, copy in the rest of the sources
 COPY . .
 RUN cargo build --release