Revert "start building enzyme on x86_64-gnu-llvm-{19|20} builders"

This reverts commit 1302345.

Author: ZuseZ4

src/ci/docker/host-x86_64/x86_64-gnu-llvm-19/Dockerfile

@@ -52,7 +52,6 @@ ENV RUST_CONFIGURE_ARGS \
       --build=x86_64-unknown-linux-gnu \
       --llvm-root=/usr/lib/llvm-19 \
       --enable-llvm-link-shared \
-      --enable-llvm-enzyme \
       --set rust.randomize-layout=true \
       --set rust.thin-lto-import-instr-limit=10
 

src/ci/docker/host-x86_64/x86_64-gnu-llvm-20/Dockerfile

@@ -52,7 +52,6 @@ ENV RUST_CONFIGURE_ARGS \
       --build=x86_64-unknown-linux-gnu \
       --llvm-root=/usr/lib/llvm-20 \
       --enable-llvm-link-shared \
-      --enable-llvm-enzyme \
       --set rust.randomize-layout=true \
       --set rust.thin-lto-import-instr-limit=10