Fix ARM images (#2302)

Allow for native building of Docker images. Use buildx if
cross-compilation is needed.

Dockerfile.arm

@@ -1,5 +1,3 @@
-# Requires binfm_misc registration
-# https://github.com/multiarch/qemu-user-static#binfmt_misc-register
 ARG DOTNET_VERSION=3.1
 
 
@@ -23,9 +21,7 @@ RUN find . -type d -name obj | xargs -r rm -r
 RUN dotnet publish Jellyfin.Server --configuration Release --output="/jellyfin" --self-contained --runtime linux-arm "-p:GenerateDocumentationFile=false;DebugSymbols=false;DebugType=none"
 
 
-FROM multiarch/qemu-user-static:x86_64-arm as qemu
 FROM debian:stretch-slim
-COPY --from=qemu /usr/bin/qemu-arm-static /usr/bin
 RUN apt-get update \
  && apt-get install --no-install-recommends --no-install-suggests -y ffmpeg \
  libssl-dev \

Dockerfile.arm64

@@ -1,5 +1,3 @@
-# Requires binfm_misc registration
-# https://github.com/multiarch/qemu-user-static#binfmt_misc-register
 ARG DOTNET_VERSION=3.1
 
 
@@ -23,9 +21,7 @@ RUN find . -type d -name obj | xargs -r rm -r
 RUN dotnet publish Jellyfin.Server --configuration Release --output="/jellyfin" --self-contained --runtime linux-arm64 "-p:GenerateDocumentationFile=false;DebugSymbols=false;DebugType=none"
 
 
-FROM multiarch/qemu-user-static:x86_64-aarch64 as qemu
 FROM debian:stretch-slim
-COPY --from=qemu /usr/bin/qemu-aarch64-static /usr/bin
 RUN apt-get update \
  && apt-get install --no-install-recommends --no-install-suggests -y ffmpeg \
  libssl-dev \