Revert "Try another thing"

This reverts commit 319ec3e.

Author: martell

ci/docker/x86_64-unknown-linux-musl/Dockerfile

@@ -8,7 +8,4 @@ RUN apk update && \
   make \
   gcc
 
-# TODO: change to stable once it has been released for musl
-RUN wget https://static.rust-lang.org/dist/rust-beta-x86_64-unknown-linux-musl.tar.gz
-RUN tar -xf rust-beta-x86_64-unknown-linux-musl.tar.gz
-RUN sh ./rust-beta-x86_64-unknown-linux-musl/install.sh
+ENV CC_x86_64_unknown_linux_musl=gcc