Remove mimalloc workaround (#4606)

- libatomic linking for armv6 has been fixed in 992c9da4c5

docker/Dockerfile.alpine

@@ -67,8 +67,6 @@ WORKDIR /app
 
 # Environment variables for Cargo on Alpine based builds
 RUN echo "export CARGO_TARGET=${RUST_MUSL_CROSS_TARGET}" >> /env-cargo && \
-    # To be able to build the armv6 image with mimalloc we need to tell the linker to also look for libatomic
-    if [[ "${TARGETARCH}${TARGETVARIANT}" == "armv6" ]] ; then echo "export RUSTFLAGS='-Clink-arg=-latomic'" >> /env-cargo ; fi && \
     # Output the current contents of the file
     cat /env-cargo